There's three things to consider mostly:
-- Frequency competition and
-- Volume competition and
-- Spatial treatment
Carving out space for the vocal via EQ techniques ... dipping certain competing instruments that intrude on the pocket -- is one method.
For instance, bass and kick don't have a lot of dominant frequencies in the range of a vocal, so creating space with them isn't critical.
Piano and guitars though ... well, there's some direct frequency competition for you.
If you pan either WAY off to the sides, you might not have too much trouble with direct competition, but as you move the competition more center, you're going to have to make some room freq-wise. Generally, it involve taking a parametric w/ a wide Q and creating a slight hollow in the area needing carving.
Once you've addressed that, you can move onto volume issues. Having a vocal stay stable ... from a whisper to a scream, involves compression -- usually on the heavier side too. Generally, with vocals, go for a compressor w/ a slower attack and quicker release with medium sustain. Set the threshold appropriately low enough (avoid draining the life out of things -- you want it to work w/ a little coloration as possible and not drain the life) and then liberally apply make up gain to even out the delivery. This is prevent soft passages from disappearing under the music bed.
Lastly, space is important. Delays and reverb cue the ear to depth and distance. If you mix a vocal with lots of reverb, and the snare quite dry, you're actually tricking the ear into believing the vocal is standing further back than the snare. Consequently, effects on vocals should be able to add space around the vocal, which sits it in the pocket better -- but avoid drenching if you want the vocalist to stand out in front of everyone else.
Think of effects a "blurring the edges" of the vocalist ... thus fitting/moving the performance more "into" or "distinct from" the underlying musical bed.
For an example of my discussion here, check out my "Sooner or Later" further on down this page to get an idea of what the results of the above techniques are.
... and like anything ...
Experiment and "practice, practice, practice" ...
Best,
Kev-