I'd like to briefly go over a simple but often overlooked punching technique used to set up a big hook or straight- Watch the old Fedor vs. Tim Sylvia footage:
Watch at 18 seconds- Fedor hits the front hand of Sylvia right before blitzkrieging his ass into the ground. It's not a one-off move that he does: you can see him do it quite visibly against Big Nog a few years back, and Lyoto Machida does it all the time.
So, how does it work? It's just a really, really simple way to distract an experienced opponent. An inexperienced guy would have a hard time stopping a barrage of punches coming straight at him, but at a pro and even amateur level, people can protect themselves from direct blows most of the time. So, a good way to close the gap and KO the other guy is to distract him, and this technique does it quite well.
1. Check your stances, because this will determine how you attack.
2. If your lead hand is on the same side (southpaw vs orthodox), hit the back of the hand. If your lead hand is on opposing sides (same stances), hit the inside of the wrist.
3. As your hand moves out to punch, lunge forward. A big component of this move is the fact that it distracts your opponent momentarily from seeing that you're closing in.
4. Start swinging for the fences. If you can't get it within a couple of shots, jump back out.
Simple and effective- try it out.