Instrumentalists only need to know three things:
1. Keep your muscles relaxed, tension in any part of your body will kill your playing.
2. Approach your learning experience objectively. If your blender breaks down, do you just keep trying to turn it on until it works? No, you get inside it, find the problem, and fix it. Likewise, when you can't play something, the answer is not "keep practicing". Find out what's stopping you and train that thing individually until it improves, then try again. Maybe you will have to entirely reconsider the way you approach speed picking, for example, but becoming a good player is all about climbing those little hills one by one until your skillset is prepared to face what you're attempting.
3. Try to push yourself with each practice session. Don't just play the same songs over and over once you've learned them, or keep playing the same types of songs. Expand your repetoire (yes, have a repetoire) and try to learn something a little harder each day.
Those three rules make lessons next to useless. Curiosity about any techniques or methods can be sated by reading on the internet and watching tutorial videos. #2 and 3 can be applied to visual arts training as well.