Here's another oil portrait for head painting class; this will be our last one using the pick-out technique, which is using only burnt umber (or an equivalent dark paint) and then using thinner (ideally gamsol) with brushes, rags, and cotton swabs to pick out your lights. It's a really powerful and fast way to work in oil, if you're doing a sketch or an underpainting I would definitely recommend it. It's also an excellent way to get a feel for different brush strokes, get used to the feel of oil paint. You'll also push your understanding of values since there's no color to be concerned with.
If you want to give this technique a try, definitely try to focus on how wet (saturated with thinner or paint) both your brush and your canvas is. Through a little practice, you'll be able to use the wetness or dryness of both to control your edges; wet brush on wet paint will push things around really harsly and create hard edges. Gently sweeping across a dry canvas with a dry brush will soften edges, slightly lighten your darks and darken your lights, letting you smooth out harsh strokes and emphasize the larger forms in your piece. In the portrait above, I ended up focusing way too much on the smaller forms of the face, the nose and wrinkles and such, so it ended up looking very flat; then to save it I did just a bit of dry brushing to re-establish the big egg-like form of the head, which subordinated all the smaller forms and made it much more structurally sound.