Hand claps are way harder than they should be...
* Get the right amount of people. Hand claps with one person can be simple, but songs usually call for more than one.
* Decide on the amount of meat and air. Some songs want flatter palms than others. Some songs want different people simultaneously doing both.
* You probably need heavy compression. Fast attack and release. Natural claps usually can't stand up to a drum kit.
* The big one: Keep the clappers around for as many takes as they can stand. Edit the good claps together. Most people aren't professional clappers. You will be surprised how rare it is that all of them hit correctly together.
It also depends on the sound you're going for.
I've done a bit of recording with my uncle and my dad, and one song we did was a mid-to-fast tempo acoustic blues sort of sound. There was no percussion, but something about it had a very "live" feel to it, so I proposed overdubbing what sounded like a bunch of people in a bar clapping in time, on the 2 and 4 of the beat.
I just used a X-Y array of SDCs, simply because they happened to be convenient, and did three or four takes of the three of us clapping along. I moved us around a lot - one from a foot or two back from the mics, one from maybe 6' back, and one from the far side of the room, as far away as I could get us. Combined, this gave a pretty decent sense of space. Furthermore, Chibi is right in that not all of the claps were 100% on the beat, but given the vibe we were after (a slightly rowdy bar crowd), it actually fit the performance much better than a bunch of machine-precise handclaps would have, and gave it a lot more "depth" somehow.
We then all sort of broke into applause and cheering at the end of the song - it was actually a lot of fun to overdub. After the first pass, my dad and uncle kind of looked at me funny, like "Drew, what are you thinking here?" but once we got a few more takes down, it really sounded pretty cool.
Given the sound we were after, I really didn't do very much to them - I may have added a bit of compression, but I don't think I did anything more than maybe a bit more room reverb, especially on the more distant take.