OK, here's my biggest help to all you fellow furniture lovers . . . don't skip the primer! I've tried to use paint+primer combo's, and so far I just haven't been happy with the results. And just going straight to paint can give you bleed through or sticking problems.
If the paint is in really good shape and not peeling or anything, I just give it a light sanding and use oil-based Kilz in a spray can since I can't use both oil & latex based products in my gun--I don't do this very often, most pieces I get are real antiques that need to be stripped down.
The last part of priming is a light sanding with a fine grit general use sand paper--general use sandpaper has oxide in it which helps to keep the paint from adhering to the sand paper and clogging it up. I like to use something like a 220 here. Give it a quick wipe down and you're on to the next step!