A scale is just the notes that are in a chord played one at a time instead of together. That's what has allowed me to go through the possible notes that work with a chord and make choices about which ones I like best. I go through by ear; you can do it by theory too, but the best way is to learn by ear.
When it comes to vibrato, a lot of people look at their hands when they do it. Which is pretty much of no use. Because vibrato is one of those things you have to hear. There are some guitar things where the visual is really useful, like seeing chord shapes or scale patterns. But vibrato isn't one of those things.