I'm busy working on my new comic, Date Night, so I thought I'd show my process from thumbnails to finished page! The page I'm going through is NSFW fyi.
I'm a visual person by nature, so when I start a new comic, I go straight to thumbnails. I thumbnail the entire comic, and THEN write down the script. I usually do 4 thumbnails to a regular page(and draw them in backwards order because I'm left-handed and don't want to smudge them).
I might do a number of different thumbnails before I'm happy with the flow and pacing, then write down all the actions and dialogue before I forget what I had in mind and have to go go back and read my handwriting or try to figure out what I was doing with the doodles. These two pages turned into three when I was transitioning to the next phase.