I know some people plan everything beforehand, and even do preparatory paintings, but I'm a great one for letting a painting evolve on the canvas, reworking it as I go along. So, the first thing I'd do is get rid of the blank canvas. Take a broad brush, the three or four main colors you see the painting having, and block in very broadly the areas these will go in (ending up with something like this).
Then I'd step back and study it for a while, thinking about the next step which is to refine the shapes and colors. (I usually sit in a chair from which I can see my easel, having a cup of tea at this stage.) Then have another round with the painting, getting more specific with the shapes, but don't use too small a brush. Use one twice as wide as you'd instinctively pick up (this helps keep the painting loose, rather than getting tight and detailed at this early stage).
Then I'd sit back again to study what's been painted and the reference photos. Then have another round at the it, again with not too narrow a brush. Finally, pick up a smaller brush and put in details, lightest highlights, and deepest shadows.
Remember, the Works in Progress folder on the Painting forum is perfect for getting feedback as you work on a painting.
