well here's general rules i go by, obviously it depends on what samples ur using, and my mixdowns are by no means perfect, but since learning these things they've definately improved..
just or the record these may be wrong in other peoples eyes, maint hing i can say is use your ears
kick cut it about 60Hz, boost at 100-120ish
snare cut about 100 Hz boost around 200Hz (for a punchy snare)
hats cut everything below 500Hz or less?
usually to make room for your snare cut the mids of your synths..
Hope some of it helps.
peace