For complicated compositions such as this, griding the canvas is the best way for me to make sure my drawing is correct and to scale. I grid the photo on my computer and use it for reference when drawing my subject.
Before I draw off the painting, I stain my canvas with oil paint diluted with mineral spirits. I used Cadmium Red Dark on this canvas. Once it dries (usually a day) I am ready to draw. Using vine charcoal is best as I can easily wife off mistakes using a tissue.