Black and white sketch
I produce a more elaborate sketch in Photoshop, using only black and white. I prefer to use a brush with Opacity turned off, so I can focus on positive and negative spaces. This also helps me develop contrasting elements. When I draw I switch between black and white, define the masses and then add light to surfaces. This creates volume and light direction quickly without spending too much time on details, and results in plenty of interesting shapes on the canvas. The brush I use is a standard one with a slight rotation on Pressure and Size. The edges are sharp and this helps me to create strong shapes.