Chopping bars (or half bars) helps. Or chopping just at drums, like snares and kicks (should be in some increment of a bar but they arn't necessarily all going to be equal length chops) is a common way. That's how i do it, just chop at the drum. So if you hear a snare hit, make the beginning of your chop on that snare. However, you will have to chop places that arn't drums or else you will have a snare sound on every chop.

These videos may apply but none are all that in depth....
http://www.3rdstop.com/viewtopic.php?t=256