Here's a bit of the process I went through in creating one of my latest images, Werewolf Attack!
I started out with a pencil sketch. This one has my original scanned pencil sketch with a few added digital layers. I was playing around with different head shapes and the direction some of the werewolves were looking. Everything was really rough and loose at this stage. I like the movement and energy these rough drawings have.
Here's the first rough version of the color block in, or flatting, stage. At this point I was really just going for overall value and trying to figure out the basic palette. I wasn't very far along when this version was saved.
ThAt this stage I've got the blocking done and I'm starting to refine it more. During this part of the process its good to keep the image fairly small on the screen and work on overall value throughout the whole piece. Its usually not a good idea to zoom in and work on small details because it can throw off the balance of the composition. Its a good idea to keep it small and work with one or two basic brushes at this stage, just to slowly build up the value ranges and keep the focal points from getting lost. This part takes the longest. Once you get your overall values correct, then you can zoom in and refine areas, but its good to keep some areas less detailed than others. The focal points should have more refined detail to keep the eye focused on the important action!
Here's the final version of the illustration. I hope you like it!