I'll add that, if you want to sort the high end, you can also go the substractive route and carefully cut high end from most/all instruments rather than boosting some - if you are trying to achieve a soft soothing sound like in ambient music, or if you want very subtle activity in the highs with hi hats and stuff. In that type of mix you might want to use peak/bell EQ for any highs boosting rather than shelves.
Yes this would also work. grapdefluid, if you follow this quoted approach, then your whole track will sound more consistently dark, and the mix will be a lot more cohesive.
Of course, if you cut highs everywhere, you have to be very careful about low-cutting and mid-range EQ, otherwise you can get some serious mud and the whole thing can blow up speakers. Also be careful to not cut too much - you can play with filter slopes to let out the tiniest bit of high end to preserve some presence.
I'm not too sure about the blowing up of speakers so I won't speak on that. As for midrange mud, yes you have to be a careful about this, sometimes people put too many musical notes and sounds in the bass and midrange when making already dark tracks.
Good advice ~ jon patch ~!