The best way to paint the ceiling is to cut in around the ceiling line allowing half and inch or so to go on to the wall. This will make it easier when it comes to cutting in the wall. Then start painting the ceiling, starting in the corner nearest to the window. This will allow you to see where you have painted when using Rich Matt as the light will reflect from the window on to the paint.

Unless like me you are using Dulux Magic White which is applied as a pink colour but will dry white allowing you to see exactly where you have painted.