I just began a new painting and realize that I have less anxiety than I used to about beginning a painting and getting it right at the first session. I’ve discovered that it’s not so important how you begin (within reason!), but simply to begin. So much about painting is about comparison (the canvas to reality and parts of the canvas to others.) Until there is paint all over the canvas, you can’t properly judge values and colors. It almost doesn’t matter what paint that is, as long as it provides a basis for comparison. It’s much easier to look at something you already painted, compare it to the set-up and think ("that’s a lot redder than the set-up. I know how to fix that!") than to stare at the canvas and think ("What red of all the possible reds should I mix for this area?") Partly it’s that colors are affected by their surroundings, and partly it’s that you sometimes (usually!) can’t figure out what color is right just by looking at reality. Pigment is so different from light that it takes a lot of interpretation to translate what you see to which pigments can mimic it.
Another reason that I like the method of putting down your best guess and then correcting as the painting progresses is that it results in several layers of paint, each getting progressively more rich. After the first session, I might correct an area by putting down a scumble . The next time I might add a glaze. These layers intermingle and can produce a result of great subtlety and beauty. Often, I plan for these layers, for example, putting down a darker area, knowing that I will scumble over it with a lighter tone later.
I have also noticed that as I progress with a painting, I begin to see more and more. I get to know the set-up, and can do a better job of painting it. What I could see at the first session seems inadequate.
So, a many-layered approach works best for me. It takes the pressure off of me to be brilliant right off the bat, and also can result in a beautiful painting!