required · Book
Universal Principles of Design Reference
Why here. Start by building vocabulary. You cannot improve what you cannot name, and this gives you a name for every effect you are about to study.
What to extract. The Gestalt principles, the aesthetic-usability effect, and signal-to-noise. Do not read it cover to cover; read those spreads and skim the rest.
How to study it. Treat it as a lookup. For five principles that grab you, find one example in an app you use every day.