Despite working digitally, I always prefer my projects start on paper; I find that sketching in a sketchbook always produces a more natural character with more thought out design choices.
I scan my images using an Epson home scanner at 400 dpi, as my preferred sketchbook size is 6x9 inches and only takes up a fraction of the scanning bed; If the scan is detailed enough and depending on the tone of the project, I will sometimes make the decision to move directly into color using the sketch as a multiply layer. Otherwise, I move on to...
Within Sketchbook Pro, I go over all my lines to make sure they're crisp and ready for coloring. I have a few preferred inking brushes I've created, and Ill link them below for anyone interested-- they add just enough variation to the edge of lines to appear more like micron marker on paper when viewed close up.
I start with color flatting all the main shapes in the image, then adjust saturation and hues to make sure the whole image will work well against a background (ill usually throw a test background layer in just for lighting reference. Then I render the shadows and highlights on each layer using cell shading for shadows and a light watercolor brush for light gradients.