I recently started to experiment with dry brushing, it is a technique that allows you to make paintings that look like drawing in a fraction of the time. This technique is particularly efficient to make soft edged shading.
Portrait painting tutorial and video for dry brush painting technique
For dry brushing you need a few stiff brushes to paint details and one or two soft round brushes for shading.
Paint brushes for dry brushing
What works well for me is to spread a small quantity of oil paint on a piece of cardboard, then rub my brush on this paint, and dry if a bit on a paper towel before painting on the paper.
Taking paint from the cardboard and drying the brush on the paper towel
I find it surprising but you can quite easily erase the paint on the paper with a kneaded or regular eraser, this is very convenient when adding highlights to your portrait.
I used watercolor paper with a very fine texture, you can also use bristol paper.