First off, I am not totally new to oil painting, but I don't know too much. I am attempting to paint an outer space themed picture with oil paints on canvas. I have the necessary supplies, and I have applied a base coat of burnt umber mixed with pthalo blue. I used a quick drying medium and left it there for a while. For this whole time, i have been constructing an image in my mind of what i plan to paint. Any tips or things I should keep in mind? I really have no idea how to go about the actual painting or the transitioning from different colors and values.