I don't have a formula but this is a fairly typical start to a painting. I've blocked in most of the areas with the exception of the roof of the building. I started by placing the main shapes on the panel with diluted warm reddish brown and then scumbled in the darks in the shadow of the boat shed, the boat on the bank and the undersides of the docks and foreground boats. I laid in the red sail as it is the focal area followed by the greens. It is basically a composition made up of horizontals (the greens and the blue-greys of the sky and water) broken by the verticals of the masts.
This is not the best photo - it came out a bit dark but it gives a suggestion of the finished painting. I wish I had photographed it in between the two stages. I think I would have liked it better one stage before this one......
