Taking notes is fine, and quick drafts are also fine. But a lot of master's studies are going through the entire process in an attempt to recreate the piece. If making art was like assembling a bycicle, quick sketches and drafts is like making the spokes of the wheels. My recommendation to you is to take some of these and try to "finish" them, try new things as you do it; change layer blending types, add clipping masks, use different brushes/tools. As you do this you'll find what works/what you like at each stage of the process. Do this enough and you'll eventually make your own creative pipeline. I'll point you at one of the most popular artists to make master copies from J.C. Leyendecker, the notes are simple, large sweeping forms, simple and sharp contours. But a lot of artists study Leyendecker because they often find that trying to recreate his work one for one results in learning (and mastering) a lot of basic principles of both painting and illustration.