I suggest try writting something that breaks these rules. Example, use F as the dominant re-occuring note in your melody and play over a couple of Cmaj7 chords in the harmony. Make it work. I bet you'll discover something very cool sounding. This goes for every rule that you encounter, learn them and then break them.
When it comes to learning theory from one person's perpective. Your basically learning how they approach theory (especially when they meantion something like "avoid tone"). This is what they have learned from there practices. But keep in mind everybody approaches music in a slightly different way.
I, myself, tend you look for what can be done, and not what shouldn't be done.
"My whole life is a dark room...ONE BIG DARK ROOM" - a.f.i.