i would say some general guidelines would be:
1. error.
we humans are not perfect, we make errors. we can't hit drums with precisely the same velocity every hit, so vary it, and the idea of raising the velocity during intense sections like chorus is also good.
more on error, not just velocity - drummers make mistakes. they're not going to be exactly on the beat all the time. i'm not saying make your drummer suck, but an occasional miss or slightly (very slightly) late hit might make it sound realistic. keep them to a minimum to make your drummer sound "good".
also repetition... if it sounds too "looped" that might be a clue something isn't natural about it, and real drummers tend to vary it up a bit.
2. limitations
drummers have 2 arms and 2 legs. try to keep at a maximum of 4 simultaneous actions, perhaps 5 or 6 stretching it with cymbals and toms. they're human, not octopuses.
3. tone
this is highly, highly subjective unlike the first 2 points. personally i'll kick out a midi, save it as audio, and bring it back into the mix. i'll then mute the midi version, and add subtle effects like a bit of reverb to the audio version to make the set sound real. sometimes you don't have to do this if the samples already have it, or if the program can do it for you. lastly EQ/pan- just the basic point that your different drum kit pieces should not all sound the same volume or velocity or sound like they come from one place...