Try studying a little bit about "track seperation".

It is certainly far too advanced a subject to cover on a message board (I was 5 or 6 years into my pro recording experiences before I had a TRUE grasp on the subject).

'Panning' can help, but certain frequencies of the instrument,s timbre will develop sonic latency the more you 'pan' the track. (Some frequencies are considered non-directional when panned, and others will be victim to phase cancellation, etc.)
The more you experiment with EQ'ing, you'll find what works with certain instruments; and what NOT to use.

If a solo guitar track (for instance) sounds phFAT in the mix, and a little bit lacking in the "low-end" when in solo-cue, then you're probably getting close to a decent guitar sound that can be "seperated". You find a low frequency that's just above the one that gets "lost" in the mix, and search to implement it in small increments using a more 'narrow' bandwidth.

Sympathetic resonance can explain why some frequencies get cancelled from an instrument if the bandwidth of the EQ is too "braod" and clashing with an instrument that's more isolated in its own timbre (such as a bass track that's real solid or heavy). THAT bass track can be used for retrieving frequencies 'lost' or subtracted from the guitar track (which you would've done to isolate it for better track seperation).
A guitar track with the typical "mids-scooped-out" can sound cool all by itself, but the track is LOST as SOON AS the drummer hits the snare!

A little experience in this field, and you'll start to see why pro engineers use compressors sometimes on ONLY CERTAIN FREQUENCIES for different instruments.

QUALITY near-field monitors can make a dif' as well ;)


~JSV