Step 1: I begin with a pencil sketch (oftentimes a thumbnail and then a sketch, but in this particular case, I skipped the thumbnail). I use a blue pencil, but I figured I'd switch it to greyscale here so you can see the lines more easily. My blue pencil lines are usually pretty light and loose.
Step 2: I ink over my pencil lines with a Faber-Castell Pitt brush pen. I'm not the best inker in the world, so I rely on my coloring to hopefully make it look halfway decent in the end. :)
Step 3: I scan my drawing into Photoshop. I have a small scanner, so if I draw on an 11"x17" (like I did with this one) then I scan it in pieces and have to assemble to image in Photoshop. I use the adjustment settings to get rid of my blue pencil lines so that only the black brush lines are showing, and clean up the art a bit if need be.
Step 4: I create a "multiply" layer and add in all my color flats. I basically just take my lasso tool and use it to select areas then fill them in.
Step 5: I add in my shading and some details, such as the girl's eyes.
Step 6: I throw some color in the background, add some coverups and mess with opacities, new layers, shines, etc. Honestly, this is where I start to do the most experimenting and playing around. Happy accidents. It's the beautiful thing about digital coloring.
Step 7: Typically I'll do at least a little bit of color adjusting at the end. There are features under the "image" option in the toolbar, or "photo filters." They can really breathe some extra life into your art -- make it warmer, or more gloomy, or colder. Anyway, once I've played a bit with the color adjustments, I'll do last-minute edits here and there, and that's about it.
Obviously, there are a trillion different ways to do digital coloring. I'm not claiming my methods are the best (I know they're definitely not the fastest). You just have to play around and find what works best for you, with the tools you have. Learn from my mistakes! Haha :)