A big problem I hear in music these days is big, flubby bass tones, harsh highs and overly round mids. Using eq is as much technique as it is taste, and using it properly can seem counter-intuitive at times.
For starters, don't solo things and eq them until they sound great. I mean there's no harm in soling something and hearing it back to you naked and alone, but that's not going to tell you anything in the grand scheme of your mix. While it may sound amazing on it's own, it will quickly get lost in the mix or be overpowering.
Start out by thinking, and leave the [virtual?] knobs alone. Listen to what you want to eq - there must be a reason, or you wouldn't be reaching for those knobs. Learn to identify what you are going for instead of just thinking it sounds wrong. Be specific, try not to get lost in the "needs more bass" or "too much high end". Think of things like "the kick drum needs more attack" or "this guitar is cutting through too much". Identify specifics in the sound that you'd like to change.
Here is a common example - the kick drum. People obsess over finding the "perfect" kick sound and I think more often than not kick drums are eq'd to the point that it hardly sounds like a kick at all, and more like a frequency-stealing, overly tubby entire-low-end-of-the-mix. So our imaginary kick drum is your average, tuned pretty well 22" kick with a hole in the front that we've crammed a shure PG52 into. We've decided that it needs more oomph in the low end and more attack. It's also a little tubby and so it needs to be tighter for our upbeat track we're working on.
First things first, we'll work on the attack. That will get it sounding a bit tighter because there will be a more apparent beginning to the kick. We take our eq, set the Q really high so we have a narrow width, and we drop it all the way to the bottom and sweep it until we find the frequency that the attack is - just loop the kick, and sweep around until the attack disappears. Bring the eq back to flat, and gently scoop out frequencies around the attack until it sharpens up to how you like it. Basically by scooping out the crap you don't want, you make your source more defined. Next we cut off the lowest frequencies, say a high pass filter [or low cut filter, depending on how you interpret it] around 60hz to cut out the rumble, and then reevaluate the low end. It may sound beefier just by removing some of the waste between the lows and the attack - if it needs a little more we can add a few DBs either by boosting specific frequencies if that is what it takes, or by choosing a low shelf pattern and boosting up the entire low end. Another option would be filling out the sound by putting on a good compressor - this can beef it up as well. Lastly I would either put a gate on it to determine the length of the kick or use my compressor setting's release to determine the length - both ways provide different sounds, so try them out.
Example #2, distorted guitar. It's your run of the mill rhythm track. It's a little dull sounding. Time to boost the highs? Instead I would see if there's a build up of mids or lows. If you pull out the lower stuff, the upper end is brighter because it's not being overwhelmed by the lower frequencies.
Cutting is unique when eqing, because it works in opposites - this may be why people have such a hard time working with it. Cutting produces a much more natural sound than boosting because you aren't adding anything that isn't already there. You can cut many more db before it starts to sound unnatural by cutting than you can by boosting.
Other EQ tips:
- Cut and boost using broad strokes; sharp boosts and dips draw more attention to being altered than broader ones. When you are cutting you can get pretty surgical but when boosting you want it wider otherwise it begins to get honky or fake sounding
- Dip out frequencies that aren't produced by the instrument to clean up your sound, for example on my mandolin I often use a filter to drop out below 300hz to eliminate some of the rumble
- Eq things in context; eq them "in the mix" for best results when mixing tracks and shaping your tone, and soloed when using eq to correct problems like sibilance and string squeal
- Vary the types of eq you use; there are many eq shapes, learn which ones are better for which tasks and use them all to vary your tonal options. Different eq brands will have different tones as well, and doing the same thing on different eqs may yeild different results
For the most part, parametric eqs are used for taste, and graphic eqs are used for fixing. Learn to use both effectively, and your mixes will sound a whole lot smoother with more space for every instrument.