The thing you gotta remember is that you need to leave enough space (in the frequency spectrum) for each instrument. Say you have a guitar, maybe you should take out some of the lower frequencies to leave space for other bassier instruments.

There is a rough guide of EQ on different sources, I will try to dig it up.

i belive mixing is something you learn from expirience same with mastering maybe,books will teach you the basics but will never make you a complete "mixing enginier",mixing 200 tracks and facing different diffeculties and problems will :D

I stumbled upon this great step-by-step tutorial on how to mix a pop song and found it most informative.
You definitely got to check this out if you haven't allready.
Greetz...

http://www.audiomelody.com/Tutorials...troduction.htm

I really enjoyed reading those mate. 8)

Always glad to provide some usefull information :D
Greetz...