Em... Sorta one page at a time? I will script in batches (one chapter at a time), which means I MAY also do thumbnails (I should, but I usually get lazy and then pay for it when things don't add up). Then I work primarily on one page at a time, but I may leave that page if it's giving me issues and work on the next few pages, doing rough drafts and such. Usually that jogs my brain and I can go back to working on the main page.
It's A LOT less efficient of a workflow to do one page at a time, but, eh... I was working in batches and I ran out of steam because I didn't get the instant gratification of having something shiny and completed every couple weeks. x.x Also because my nerves and muscles are all borked up, I can only work in short bursts anyways, so there's no point in having a long workflow.