Please also keep in mind that while it is commonly referred to as ‘Fisting’ - that this is largely a misnomer. Technically, the hand is open with fingers straight, not clenched in a fist… only experienced players can enjoy a clenched fist.. commonly refered to as “punch-fucking”.
These are only my thoughts, experiences, tips and tricks when it comes to handballing:

MINDSET
If you really want it, then you should be able to take it. This goes for everything from dildos to baseballs to baseball bats to billiard balls to fists… to small convertibles and stretch limos. There are very few men that I know who are physically and/or medically unable to take something up their manhole.
In my opinion any and all anal play, from vanilla fucking to fisting, is largely a mindtrip… There are days when I can't even stand the thought of any insertion of any kind and even a fart bothers me… there are days when anal sex of any kind is all I crave - more more more now now now! ;o)~
Despite the fact that handballing is a physical event, it is mostly a mental trip. It is trusting your Top and letting him know you trust and appreciate him putting his hand inside of you. The physical act of fisting, while intense and addictive, is simply the physical mechanics of the actual mindtrip. It's difficult to explain… if or when I formulate a better way to state this, I’ll let y'all know.
COMFORTABILITY
Do NOT try to force anything up your manhole. If it hurts… slow down or stop. The expansion to take a hand may be an uncomfortable pressure/stretching.. initially, but it shouldn’t cause pain. Start with toys. There is nothing wrong with using progressively larger toys and switching back to a smaller toy if your body isn’t ready to receive the larger toy.
If you don’t have complete trust in the Top to relax your hole at your pace, but most importantly to stop when you say stop - do not attempt this scene. If your Top is not willing to take the time to work your manhole (and it DOES take time…) , then don’t start the scene.
Fisting videos normally only show you the actual fisting because… let’s face it, that’s the hot sex you wanna see! They don’t show the 20 minutes to hour(s) that it takes most bottoms to relax the manhole with toys and work up to a fist. Most of the fisting bottoms in the videos are 'professionals’ - or handballing is their preferred anal pleasure - and they know how to get to that space quickly.
PLEASE do not, as a bottom or a top, take your cues from porn videos and rush into an insertion.
CONCERNS
1. Permanent Stretching - NOT!!! Contrary to urban legend, you don’t remain 'loose’ for the rest of your life and you can't 'break’ your asshole so that it will never tighten up again.
Your body truly is remarkably resilient. Your sphincters do contract back to their original tightness. It is my experience that If anything, you get tighter due to the routine exercises and the rebound effect of stretching your manhole to accommodate a large object. It is all muscle control - learning to control your manhole to accommodate large or small insertions. My former husbear used to tell me to “Clamp down nice and tight on my dick!” and moments later, “Relax your asshole, man, or you’ll cut off my dick!” Then he could turn around and fist me the next time…Then complain that I’m too tight the next time he fucks me, heh heh… I hear the same thing from my current play mates. So, I don’t subscribe to the speculation that fisting ruins and permanently stretches your asshole.
2. Tearing - Yes, you can tear, severely in some cases, if you do not take adequate time to reach the relaxed mental and physical state where a fist can be received. This is why I state that the receiver should never force anything up his manhole. Even after adequate time with progressively larger toys, you can still expect a tad of bleeding if you try to force the situation. Do not let your lust for the feeling to override your common sense.
3. Pain - Any anal play will involve a bit of initial uncomfortableness getting past those sphincters, but not pain. Fisting should not be a painful experience if you take the time to work up to it. Fisting is only an extreme extension of getting fucked… it should be pure mental and physical ecstasy!

TIPS
1. FEAR - All I can say is this; Get over it!
If you want to experience getting fisted, you must get over the 'fear’ of it. It is no different than using a thick dildo and feels infinitely better with a nice warm hand and fingers tickling you from the inside! It took me months before I understood this and was able to let go of that defensive thought.
Getting over your fear of an actual hand inside you??
This largely depends on your Top. You must KNOW that you can trust your Top to go slowly, take care of you, and respect your limit. If he is willing to invest the time then the both of you will enjoy the scene. And trust me when I say that Tops get off on it too… Probably more than the Bottom. As a fisting Top, I have cum without touching my cock just from loosing myself to fisting a man. It is as intense a scene for the Top as it is for the Bottom.
I suggest getting over the fear of and embarrassment of wanting to play Red Hanky and finding an experienced handball Top and let him know that this is something you want to experience… Yes, I stated embarrassment. I was literally ashamed (and shamed) and embarrassed for desiring this sexual act. My desire finally overrode my embarrassment and sense of shame in wanting it. Glad I did too… WOOF! So, ask a Dom or Top that you respect about it.
Sounds silly, but Doms (along with most leatherfolk) take extreme 'play’ very seriously and most will sit and talk with you about it - or if they are not into handballing, they usually know someone who is and can refer you to that Dom or sub. The Dom or sub can tell you the proper way for a Top to relax your manhole and what should give you concerns that the Top is not experienced and could possibly hurt you. Keep in mind that many men into handballing are Sidepockets (versatile). They enjoy giving as much as receiving…
So, don’t be afraid to ask… All they can do is say 'I don't want to talk about it with you.’ If you don’t ask the questions, you won’t know the answers and could get yourself into serious trouble.
The Top that you ask just may be inclined to teach you what you want to know… and work with you on taking a fist. If not, he will probably refer you to someone he trusts to work with you on achieving your goal. Keep in mind that the leather community is a rather close knit bunch and most guys know each other - and they are usually amicable to helping those attracted to the lifestyle.
NOTE: When you do play, make sure that fingernails are trimmed and the edges are filed smooth. Even when wearing vinyl gloves, you will feel the slightest hangnail or rough edge on a fingernail. Hangnails and rough-edged fingernails lead to minute tearing and cutting and spotting (bleeding).
2. Relax - Hmm… notice how I keep pointing this out? If you truly don’t want to experience fisting, then your body won't relax enough for you to achieve this goal. If you really want to get fisted, then it takes a little practice to learn how to relax your manhole. You must work up to taking larger objects in progression.
For those of us into heavier assplay (larger thicker toys, etc…) it helps to understand that taking a fist is basically the same as taking a thick toy. Look at some of the larger dildos that you can take and measure the circumference in comparison to your wrist and folded hand. They are about the same. You can take the toy? Then you can take a fist…
Do not expect to take a fist the first few times… and don't be discouraged if or when you can’t. There are days that I want it so badly and can’t take it… There are days when my manhole sucks that hand inside so fast that it even freaks ME out! LOL.
NOTE: There are many lubricants on the market that are 'designed’ for handballing. All are manufactured lubricants (read: chemicals) and will dry out, get gummy, and can cause chemical irritation. Use whatever lube you use with your toys and anal sex. If you are playing safely and using latex gloves, make sure the lube you are using is compatible with condoms.. Some designer (fisting and anal) lubes are not compatible with latex. Latex gloves, latex condoms = same difference - so don't think you must invest money in designer fisting lubes… Just make sure to have ALOT of your preferred lube on hand - pun intended! LOL
If you are using Crisco or a lube designed for fisting… they are not latex compatible!! So… Get dressed, get in the car, drive to Home Depot, go to the Paint isle, buy a pack of vinyl gloves (in your choice of 5 fashionable colors now), drive home, get naked, and get that man’s hand UP your asshole!! NOW!!! ;o)~
Seriously, whereas latex will dissolve and break in Crisco, Wesson, (which is basically oil) and most lubes, vinyl gloves will not be affected by these products. Vinyl gloves are also a bit thicker and won’t pop or tear as easily as latex gloves.
Personally I prefer the time tested lube… a can of Crisco shortening. Clean up takes longer (Palmolive cuts through it instantly- do not use it internally! LOL), but Crisco is still my fav. It doesn’t dry out or get gritty or sticky.
J-Lube is fantastic for fisting also and can easily be washed off with salted water… And I’ve never found a leather shop that didn’t carry J-Lube.
3. Exercise - Exercise your sphincters… yes, I said sphincters - PLURAL! You have more than one! The outer sphincter and an inner sphincter about 2-3 inches further inside. The outer sphincter (your visible asshole) is the easiest to control and easiest to exercise. The inner sphincter is the one you must learn to control (stretch) using toys and fingers. You or your Top can use progressively larger toys… inserting four fingers, expanding and contracting them inside you (stretching that inner sphincter and letting it relax.) and / or a combination of the both. The added benefit of anal exercising is that not only does it teach you control over those muscles, but it also strengthens those muscles… Like I said, I can clamp my ass down so tight that nothing can get in or I can relax it to the point of taking a hand…
4. THE THUMB WAR - AAACCKKK!!!! - Obviously the most challenging part of getting fisted is… the thumb joint. Many men don’t have flexible enough hands to fold their thumb completely inside their palm and create a circumference comparable to the wrist. This is actually part of the fun, in my opinion! Think of the hand and thumb joint as an asymmetrical (odd-shaped) cock with built in French ticklers!
5. Stimulants - I seriously suggest that a beginner not use stimulants… A couple of beers, cocktails, a glass of wine or champagne is fine… Do not allow yourself to get drunk. Do not toke, pop pills, inject or snort anything. Getting 'wasted’ in any way will impair your judgment and numb your manhole to the point that you won’t enjoy getting fisted or even KNOW if you are being internally damaged.
I also suggest that beginners not use poppers. For most guys, poppers intensify (as is the job of poppers to do, heh heh… ), but the intense physical feeling could make your body unwilling to accept such an extreme insertion. If you must use poppers, use them sparingly. For some men, poppers will temporarily numb and relax the outer sphincter and make insertion past the thumb joint a breeze… And while this is true for me, in my experience, it also makes my inner sphincter tighten up… needless to say that this is not good if I wanna take a hand up my ass!
I can only state - try it and see if that works for you. If it works with your larger toys, then it may help the initial insertion of the hand.
As you all know, I don’t use drugs at all… other than a few social drinks. I don’t even keep liquor or beer in my home. And I rarely use poppers (they cause sinus problems for me). My routine is that I have a couple of Belgian beers (Chimay) to relax my head a bit, then I drink water for the duration of the scene. which works out great for me because I love pissing all over the place while I’m getting fisted SLURP ;o)~

TRICKS
1. Direction of the Insertion - It is easiest to insert and remove a hand vertically… meaning; insert the hand in correlation to your asscrack - in the direction as if shaking hands with someone. Your sphincter will stretch farther vertically than horizontally. This will allow you to take the thumb joint without a problem. Once the hand is inside of you, it feels great to twist it back and forth and around and around ;o)~ but insertion and removal of the hand is best done vertically.
2. PUUUSSSHHHH - My personal trick - Push like you haven't taken a dump in over a week! All the anal exercising and toy play will prepare you to take a hand… but that thumb joint will still pose a problem even if you are uber-hot for a hand in your hole. If you push your bowls like you’ve not shit in a week… at the same time that your Top is sliding his thumb joint inside, it will literally force your asshole open to take it.
The moment that thumb joint slides past your manhole, your ass will instinctively clamp down on the wrist. Not much you can do about that… The physical rush will make your head spin… and the realization that your man’s hand is inside of you will make you wanna faint with joy! TAKE IT SLOW! The best thing to do once you’ve finally gotten that hand inside of you is to concentrate on relaxing your asshole so you and your Top can enjoy the sensations of having his hand inside of you.
Your Top can slowly twist his hand and wiggle his fingers, but don’t have him pull out and try to reinsert his hand until you are used to the feeling and get over your initial (hopefully joyful) shock that you finally took your man’s hand! He probably won’t get his hand back inside of you if you are new to handballing.
The first time you take a hand, you will feel full… and I mean FULL. Your body’s urge is to expel the hand… this is where it is up to your TOP to gently, yet firmly, keep his hand inside of you until your anal spasms calm down a bit… This is why I state, on your first few times, to not have your Top try to pull his hand in and out of your manhole. In most cases, the first few times he is inside of you, he will not be able to get it back in if he pulls it out - your ass will tighten up when he pulls out. I suggest you learn to fist yourself and practice/enjoy taking a hand alone… Sounds difficult, but it’s really not. Or buy an Adonis or The Hand toy and play with that.
They are 100% scale to a hand. The Adonis is smaller (the size of my hand, actually) and would be the toy to try first. Most online 'toy’ stores carry them and depending on the State in which you live, you’re local fetish toy store would probably have them also.
Obviously, I’m limber enough to fist myself without a problem. But you don’t have to be overtly limber to fist yourself if you go about it the right way… heh heh. Please refer to my auto-ff fotos and vid clips and you will understand the easiest positions and most comfortable way to fist yourself.
redhankyhandball.socialparody.com/pg/forum/topic/1487726/fisting-101