I start all my work with some line art, and I am not that really good with it but t helps me to paint later. Since I was going to keep the line art for later, to get the cartoony feeling, I cleaned it a bit and refined it with a bit more details. Than I add some basic colors I wish to use, this step helps me keep the perspective on the areas in the image, I do every color on a seperate layer, and having a line art I can be more relaxed about perfection of the edges. The reason I've added blue around the body is to create stronger contrast, my eye accepts blue more than white, this also helps me keep the attention without starining my vision after five or more hours of painting. From here it's a lot of experimenting with colors and shadows, I am still not much experienced so I work slow and make a lot of mistakes. But I had a generall idea of the light source so I keep that in mind and just paint and paint.