STEP 1: Simple thumbnail sketch. I do a few really rough sketches focusing on proportions and pose. I try to do a sketch in under a minute then move on to the next one. When I spend more time on them, I start losing the initial dynamic forms.
I try to get through step 2 and 3 very quickly so I don't get tied down to anything. Now that I have the basics in, I can decide more specifics like: 'Where does this break? Where do I need to adjust proportions? Where is the light source? Who drank all my soda?' etc.