In our forum we seem to have people with audio mixing prowess ranging from newbie to professional. Take a great midi mockup and mix it poorly, and no amount of midi tweaking will make it sound right. Take a lesser midi mockup and do a great job on the audio mixing, and you might get a better result. Obviously, a pro result requires both a first rate midi mockup and audio mix.
I have personally long since given up on mastering the art of mixing - I hire pro's to do my final mixes and mastering. But, I got a major step forward by reading this book: "The Art of Mixing", by David Gibson (c 1997). You can find it here: http://www.artistpro.com . It's very well written, using an easy to grasp visualization approach to a sound mix, and covers all the basics most of us will ever need - including panning, EQ, compression/limiting, gates, delays, reverb and other DSP tools and trickery.
I highly recommend this book to anyone who wants to move up the 'art of audio mixing' curve.
I actually own this book and found it very helpful. It gives a really easy-to-understand look into mixing, though definitely not dumbed down. Gibson's visual system let you "see" your mix which is very useful.
The thing I always try to keep in mind when mixing, which is really hit upon in Gibson's book, is that you always start with a finite space and it is up to you how you fill it. Every time you add EQ to anything it increases the space that it takes up. Conversely, everytime you subtract EQ you add space for something else. Adding effects adds a whole new dimension of course.
The only thing I didn't like when I originally purchased the book was the price (it used to be around $50), but it looks like they generously lowered the price now. Definitely a good buy.