We began with the lighter shadows on the clouds yesterday, but you might want to give the body of the clouds some pale, warm color first, suggesting late afternoon light. Then, light shadows, darker shadows and, finally, whatever you want for the spaces between the clouds. If you want some white at the top of your shapes, don't forget that the paint will spread on wet paper, so leave more room than you ultimately want.
I like to leave the blue part of the sky for last, even though it means I have to wash the gray out of my brush first, risking a bloom. I know it seems sensible to start with the blue, painting around some cloud shapes,. Then I could just add color to make the gray and not have to lose track of how wet the brush is. But it works better for me to have the blue strokes be the finishing touch because then I don't have to carefully "color in" the shadows on the clouds. I prefer not to be constrained, so the brushwork can be freer - from the wrist - to feel more like the clouds just happened, and were not man-made.
What we're really doing in this exercise is developing awareness of the relative wetness of the paper and the brush, so you needn't feel bound to make realistic skies. It's all good practice. Have fun. Take enormous risks. The job is to learn, not to impress.
Here are a few sky photos and paintings to get you started:
|Methow River Basin|
Colonia La Noria, Oaxaca