As someone said about it is all about subtraction.

If you can, always cut rather than boost, it just sounds so much nicer, and when you have 50 tracks all running with eq boosts in them it all tends to sound pretty nasty. If your lead isn't bright enough try taking away some bottom rather than adding top.

it's also helpful if you have a half decent eq to start with, if you aren't sure if yours are any good, compare them with the waves plugin's which are pretty good, though blatantly if you've got a powercore card get the oxford eq plugin...

Cheap analogue desks sound particuarly nasty usually when doing big eq boosts. you can do a 16db cut on them fine, but add more than about 6db and it can start to get evil.

Kicks and basses frequently get fatter when you cut about 6db somewhere between 300 and 800 hz