Old School
Today we began to really dig into mixing, utilizing Alloy2 EQs and the Decapacitor from SoundToys. But first we reviewed the importance of organizing your work flow so that you can immediately set to work on mixing your tracks without losing time because your DAW project is not organized. Having an instructor who knows the value of your time and has a solid workflow helps immeasurably when your working out your own.
A key difference with this Mixing class is working with an instructor who is an active working engineer not a DJ/producer/musician as in most of the other courses. I don't think is realistic to assume you can fully take on mixing and mastering your projects after a 3 month course, but I do think that understanding the process, tools and the requirements that your mixing or mastering engineer need will by itself allow you to create good projects that can be improved by professionals. The key here is improved not repaired, as Ariel said today, you can't "fix it in the mix".
The class usually allows for a "lab" time when you can work on your mix with the instructor available for questions, this really makes a huge difference and allows you to make sure you know your way around the various plugins.