Depends on the genre a lot. Drums are really tempo dependent.
Some people take sampled drum fills, tom rolls etc from breaks which is a good standard thing to do
Dnb is good at drum fills- they tend to change the pattern to a more syncopated one and put FX on: phaser is common, filtering is pretty common, I've heard automated bitcrushers used to good effect.
House/techno fills are very simplistic, just add/remove one kick/hi-hat/clap at the end of each section