Do you want to really beef up your lead tracks? Are you jonesing for that huge vocal sound? Maybe you're having trouble getting a track to "sit" in the mix without sounding tacked on. This is a common problem with vocals.
You can apply this technique to other instruments as well. A cool thing to do with the kick drum is to create 2 tracks. EQ one for “snap” and one for “thump”. You can have both sounds and simply mix them to taste.
Using the track copy feature in your software make at least 2 copies of the track. EQ each track differently. Make one track very bright, leave one flat and create a track EQ'd with a lot of bass. Don't be afraid to get drastic with your settings.
Now you have three frequencies that you can simply access by working your faders. If it is sounding a little thin, blend in the “bassy” track. Too dark? bring up you “treble” track, etc…
You can also experiment with varying degrees of pan and effects. Try creating a track that is soaked in verb and then just barely blending it in with the others. If there is a certain frequency that you just can't seem to hear create a track just for that one. Then blend it in as needed. I have songs with ten or more tracks all EQ’d and effected differently…very fat!
This yields a much more of the "three dimensional" sound that you hear on most recordings today.
This isn't a "cure all". There are lots of other factors to consider, but I have found this technique to be very helpful.