Practical Mixing – from sound On Sound magazine.
This article focuses on tracking and mixing via console (with an aside to address the importance of checking a reference CD while mixing.) But Sound On Sound caters to the masses, so the information in this article is broad and still generally useful.
It is important to keep checking the balance in mono as well as stereo (or surround) — particularly if your material may end up on the radio. Inevitably the mono mix will sound different to the stereo (and the stereo to the surround), so a degree of compromise will be required to achieve the most acceptable results in each format. Pay particular attention to reverbs, which have a habit of drying up when you listen in mono.