One of my favorite things to do is painting short poses. When I was in art school we did alot of gesture drawing which was always 2,3,5, and 10 minute poses. Only rarely did we get anything longer. When I moved to Arizona, their idea of gesture drawing was some two minute poses in the begining and then 20 minute poses for the rest of the night. I decided to try painting them and instantly loved it.
I always draw with the brush. I use Burnt Umber and White and do a quick gesture sketch. Then I draw over it in straight Burnt Umber. I try not to let the drawing take more than 10 minutes on a 20 minute pose or I will not have enough time to paint. On rare occasaions, I have just left it as a drawing in paint if I like the way it is coming out.
After I get a drawing down, I then move to the shadow areas. Sometimes I fill them in in solid burnt umber to save time, other times I am more precise. If I am in my studio I tend to be more accurate, because If I like the painting, I can just make the pose longer and finish it. Can't do that in a public painting environment. I can always go back and add color to the shadows later but sometimes I like to focus on the lights. A quick pass for the halftones which are often the same value as the tone of my canvas. If there is any time left I work on the lights. Often by the time I get to the lights there are only a few minutes left.
I use a limited palette on these of: White, Yellow Ochre, Cad Red Med, Burnt Sienna, Burnt Umber, Cobalt Blue, and Ivory Black.