Start out with a blank page. The actual file is ~3000x5000px, but here it is resized for internet purposes. I always use photoshop for my paintings, but you're welcome to use any image painting program, as well as any digital tablet or mouse (I use an old old wacom tablet).
Step 2: Main sketch
First is the rough sketch, just blocking in where everything should be. Don't get too wedded to any of these lines, because half will be ignored/redone/moved/painted over by the end.
Step 3: Basic background
Now to block in a basic background. Since I'm using a purple/blue background, I just throw some yellow/orange (complementary color) over the main figure, so hopefully that will come through. This works better in oil paintings than in digital, but the principle is the same.
Block in basic shapes and colors. It's good to pull from the background for shadows, so that the background colors get incorporated into the skin/hair/etc, the way they would be reflected if you were actually standing next to a purple wall or whatnot. Remember that the skin isn't just pink - it has greens and blues and reds, and it's good to work those in as well.
Step 5: Facial Reconstruction
Corrections to face anatomy/lighting, both of which were appalling in the initial rough painting. Since it's a character I've done before, I also stop to check my old pieces to see if I'm being (semi) accurate to how I've painted her before.