OK, so one more...

Pay attention to your listening space. Your monitors/speakers are important. Your room is important. If you use headphones to mix (as I do mostly) be very aware of how much different they may sound than speakers. Just, in general, understand that your setup will be different than my listening environment so what you hear will sound different on someone's iPod or on their big stereo system or in their car. It is a good idea, especially in the beginning, to listen to your mixes on a variety of systems to see how they sound. Also, use those reference CDs!!

And, if you do find yourself mixing in headphones you might wanna try Focusrite's VRM box (http://us.focusrite.com/usb-audio-interfaces/vrm-box). It is software and hardware that plugs between your computer and your headphones and it attempts to simulate/model a variety of locations and speaker types. Plus it tries to simulate the stereo field like you would hear it from speakers instead of how it sounds in headphones. I think this device has helped my mixes.