Here's is my work process in a nutshell for a few characters. I usually do a quick sketch on plain paper and send it to myself by snapping a photo with my phone - I don't use scanners as much anymore. I try not to spend too much time on the initial sketch if I'm doing a vector piece because it's much easier to make changes in Illustrator. I'll detail the rest below!
I use the "Place" option to put the sketch in Illustrator. I lock the sketch so it stays put, then I create the layers I need, from Outline, to Colors, to Highlights and Shadows. The first step is to make the outline.
Next step is to fill in the colors. If the character pre-exists, I color pick straight from an official image so I'm not worried about matching the colors. I love single-color backgrounds because they emphasize the character in the middle.
The final two steps involve creating paths that act as shadows and highlights. These are usually on the same layer. I then add certain textures and change the coloring on some parts, depending on the look I want. In this instance, the character has some metallic parts, so I use a combination of paths and filters as well as the extremely useful gradient tool to emulate the look of metal.
This is just a snapshot of the paths that make up the character above. I hope you enjoyed my work process!
