Drawing with thinned paint and a brush I lay in my composition and block in the dark tree silhouettes and the shadowed ground area. By starting this way, I find it easier to judge the value* relationships between adjacent areas. For example. With the dark tree value established I was able to mix an appropriate value for the distant green field by placing it up against the dark value of the trees. This way you can quickly see if you have made your color too dark or too light or just right!
*Value is the relative lightness or darkness of a color and is represented on a gray scale ranging from white to black with successive steps of gray in between.