I digitally mock up the head-with-hands, and sketch it in charcoal on architect's vellum - you can see the sketch at the top. After priming the sketchbook's cover with white acrylic paint I use a brown watercolour pencil for sketching, and then dab in first strokes of the colours I want. I have cheap acrylics left I use instead of my artist's grade paints, so I won't be sorry when it eventually gets beaten up from travelling. I work on the glass pane of an old picture frame, which is easy to clean, and I can put my sketches under it, like here:
I'm going for garish colours, so I use the paints straight from the tube, expertly titled "brown" or "orange". Wonder why I want to get rid of them? I cover the entire thing in a thin wash of orange and apply reds and yellows with palette knives. Every now and then I strengthen the contours with the watercolour pencil. To paint properly, I have to prop the sketchbook up on books, with the pages between the two stacks.