Step 1 - The Layout
Seems simple enough... I don't usually have a set script in front of me of what's going on in each page, because I find it hard to visualize how much room I'll have. By the time I get to this preliminary stage though, I have an idea of what will go in each panel. It's probably better to have several pages planned out ahead of time, but if you at least know what's going on in each scene, you should be okay.