As long as your tracking correctly(i.e. getting the sounds you want on disk in the 1st place and not 'fixing it in the mix'), then mixing should be a simple process of simply sweeping to find any trouble spots.

How's THAT for a sentence :roll:

I just noticed you comment on multiband compression. That is generally used in the mastering process.
As your already finding out, the more carving you do with EQ and other signal processing, the more unnatural you mix becomes. That's why it's so important to take the time to track properly.

Is there a mixing technique that one would use to give a mix more definition between instruments. I have been using eq and shelving/cutting the lows and the highs, am I on the right track?

It depends. If it needs more definition, its either not tracked well, or the arrangement is not great(too many instuments in the same range). There are different things you can do like: Panning(where you place the instruments).
Volume changes-bringing things down or up
EQ and dynamic control-which it seems like you are trying to do. Stay away from multiband compressors and just create your own which are easier to control.
Effects
I think the most effective way to make an instrument more defined, is to mute out what ever is clashing with it. You don't have to use all 50 tracks, not everything has to be in stereo especially if one side is out of phase. Only you can make these choices. Some food for thought.

What Thrill said...

Sometimes in a problem mix, I'll stop and mute everything except the drums, bass, and lead vox. Usually there is a simplicity and clarity (and space, of course) with just those tracks that is often more compelling than hearing a cluttered mix. So now the trick is to keep that vibe even as you gradually bring the other elements back in - it may entail keeping those synth pads and backup vocals a lot softer than you originally had them - and panning those busy tambourine and shaker parts wide away from the middle.... well, you get the picture I'm sure. Less IS more. A lot of the time, anyway.