it varies alot. especially the threshhold level which should be set somewhere between the loudest and the softest peaks of the signal.
as for ratio, attack and release settings just mess around with the knobs and get a feel for them. i mostly move around a ratio of 4:1 and upwards for some heavier compression. it highly depends on you signal and drum.
one thing is for sure tho. the attack should be set at around 50ms. minimum is 30ms on drums. anything under 30 won't have any punch at all. my personal favourite release time on toms and snare is 200ms. some might say 500ms is even better tho.
that goes for close miced signals. OHs and summed drums will benifit from much slighter compression.