The best thing about a theory is that everyone is allowed to have their own individualized take on it. That's what makes it a theory! Of course there are some common guidelines that can lead to the best possible results, but there are no rules.
One of the most simple yet imperative things to remember when starting to mix is organization. Anyone who has spent any time mixing whether professionally or pre-professionally should tell you how much easier things will go if stay organized. Things like labeling and color-coding tracks, leaving markers to identify parts of a song, utilizing comments sections to plan ahead on specific tracks, and much more. Just figure out a system that works best for you.
Mixing is a producers/artists best tool to encapsule and polish exactly what they want for a song. One thing that helps us do this is the use of stereo imaging. This gives us the ability to use 180 degrees of sonic atmosphere to impress the listeners instead of one degree, right in front of you.Controlling volumes, panning, reverbs or delays can all add special characteristics to your stereo image, as well as to the image of your whole song! Just like a painter has his canvas to paint, we have this canvas to mix.