I map out the painting in a brushwork drawing in yellow-ochre wash, with a turpentine rag for removing any paint, in the other hand as I block in the idea. This light yellow wash, keeps it ambiguous, so corrections can be easily reinforced with a darker shade as I go. When I feel I have a firm foundation for the work, I let it dry. Then; I mix the color for the area colors on the palette with-clear paint medium (for ease in application). This keeps the colors fresh. I rarely mix color on the canvas, unless blending is needed. I block in the color with first abstract shapes the subject represents.  Always backing up, to get an overall study of the design, I study negative spaces as well as positive spaces, (values then colors). This, for me, is very important; more important than a finished painting. I develop the feel of the whole image, working on the entire canvas at once, never concentrating on just one area at a time. Occasionally,( I will sketch the painting placement,(options) if it is complex), but I prefer to go for it, with a loaded brush and have the exploration, part of the final piece of work.