Here is the original photo that my student, Jeanne Alexander, worked from to paint a portrait. Jeanne has a specific painting process that works for her.
She creates a color copy of the photo and makes reference marks before starting the drawing on canvas.
By connecting the dots she draws out the figure in pencil. The photo doesn't show it, but she started with a blue ground.
She covered the t-shirt and the background first.
With a varied portrait palette she blocks in the face minus features and hair.
Then a simple coat on the hair.
Eyes and nose.
Mouth and ears.
More detail on hair.
More contrast on all of it. Wonderful.