I started by paint the musician and focal point in the painting. This part is the the key point for matching the values and scale of entire painting. I used standard value steps, from light to dark, high (glittering) light, lighter, medium light, dim light in the light catching area and deepest dark (terminator), dark shade, reflected light and cast shadow in the shadow area.
My painting approach is to use relatively simple value steps at the beginning stage and to control the color temperatures later.
Sometimes when I use a cotton canvas, I use leftover paints for priming. This canvas was so primed with dark grey colors and I had to control the right initial value.