One of the factors that i used to it is trying to capture what the scene is about by a tonal value sketch, it helped me a lot. In this way i can arrange my attack in watercolor process.
I think this tonal value sketches are usually great piece of art indeed.
I see art students that do not like to do this step by step process.
I give you two examples of using tonal value and the final results.
The photo is from the book " solving the mystery of watercolor" by David taylor.