EQ AUDIO FAQ:
Answers to questions about recording, microphones, equalization and capturing better audio:
Regarding the use or overuse of EQ, here are a couple of pointers that may lead you in the right direction. The use of EQ on source material not only changes the sonic characteristic of that material (makes it sound brighter, duller, punchier, harsher etc.), but also creates a sound of it's own. Each brand and type of EQ adds it's own sound, and the overuse of any one type (especially a not-so-good type) can multiply this effect over all of your tracks causing the entire mix to sound either harsh, thin, unbalanced, phase shifted and unprofessional.
If you are working in the digital domain, using a tube parametric eq with variable q (means you can adjust the bandwidth as well as the cut or boost amount around a chosen frequency), the tube circuitry can help warm up the "digital" sound quality of say a lead vocal or guitar track. There is no one perfect eq, but having a choice of the eq in a decent console coupled with maybe an outboard eq like an api or summit tube etc.. will give you more options.
Sometimes not doing too much to the recorded sound can yield better results than just adding high frequencies and bass to all of the tracks. If you experiment with cutting frequencies that do not contribute to the mix, you will be better off most of the time making room for other instruments or vocals instead of just boosting everything creating an audio "fight" for the listeners attention. One more thing, it usually works better to eq a track within a group of tracks or the entire mix to better judge how the track is working with the rest of the tracks. It makes little sense to go for a killer sound on a grand piano in solo mode just to discover that it does not work with the rest of the track.
There are many good books and articles on mixing, and the more you are involved in it, the more there seems to be to it. But there is no voodoo or black magic involved, and simply using your ears (assuming you are listening over reliable monitors) and sitting there and mixing, you can achieve good results. I think the short answer to your question is, that unless you are going for an effect, try not to over use (especially over-boost) eq, and try to find ways of cutting frequencies instead to get the results you are after.