Some fist references! I was seeing execution of hand positions that was kinda making me cringe earlier today, so I did this up really quick. I guess useful for both artists and anyone who plans on getting into a fight, but ah well. I’d do more, but there’s only so much you can do with one hand at 3 AM when all your friends are asleep and can’t take pictures for you—
When punching, your index and middle finger knuckles should be taking the forefront of the force. You should be punching with the flat part of your fingers between the knuckles, and not with the knuckles themselves (with the exception of a few stylizations or actual knuckle strikes, which are executed slightly different from punches and generally aim for soft spots anyway). You can see here that the hand is slightly tilted to favour the first two knuckles, in a way that your entire arm can support the force landing on your fist. Not only does it keep your wrist from breaking, but it allows you to deliver a lot more force.
Again, try not to let the force land on your ring and pinky finger. It’s an easy way to break your fingers— not to mention, with the tilt of your fist, you’re likely to break your wrist as well. Tucking one’s thumb inside of the fist rather than outside of the fist can also result in a broken thumb.
Knife hands! There’s different knifehands for different styles (I assume, anyway—) and of course, since knifehands are utilized for multiple different techniques (from striking to preparing to block) there can be variations. The safest form, however, is a tucked in thumb, with fingers strong together. Middle finger is generally slightly bent (you can sort of see it in picture 7) just so that it doesn’t break— any force applied to the top of the hand in a strike thus kind of applies to all three fingers, rather than your poor middle finger alone (slightly bend makes it kind of springy, though the tops of your fingers should all align on the same plane at the tips). Pinky is not left out hanging like in 8 either— with thumb and pinky outstretched, it’s likely you’ll catch a digit on something and break it (if you can imagine, please, attempting to break a board with your hand in a forward strike and instead having your pinky or thumb snap sideways).
General defensive or preparation knife hand— usually the other hand is at a chamber (a chamber is a pre-strike held position) either at the side or beneath the sternum. Front hand is turned slightly outwards.
Wow backtracking a tad bit to punches, but arms! Don’t overextend your limbs in any of your strikes. I slightly exaggerated it here, but it’s far better to have slightly bent arms and legs than to have overextended limbs (easier to break the latter, especially if an opponent was to strike your limb at the time. I’ve seen so many bones broken this way). Overextending, bad. You’re also likely to pull something like this.
karate chop!!! Or what have you— generally, strike with the meaty part of your palm rather than your fingers (broken fingers, there’s not much of an arm to support your digits in this angle of strike). Slightly bent middle finger is okay here too— try both positions with bent and straight fingers and squeeze your fingers together and you can sort of see why (though, the force shouldn’t be applied to your fingers in this sort of strike anyhow).