Paint a few soft-edged skies. This means that as soon as you see a hard edge, STOP. Let the painting dry completely, then re-wet the area where you plan to make more soft-edged strokes.
Can you tell how many layers of paint were applied to make this sky? It looks like four to me. First, the paper was wet with clear water, then a layer of pale, warm peach color was applied across the bottom and center. While the paper was still wet, the lighter gray went down. Then the dark gray, and finally, the blue. The brush needed to be washed once - between the dark gray and the blue.
Remember to stay aware of how wet your brush is compared to the paper. And don't correct these paintings. If something goes wrong, let it be. Really.
When the paper is dry, add some hard-edged landforms. Or, on second thought, let them be soft, too. Experiment. Be playful, and have fun.
Take a look at this week's intermediate homework for a short discussion of how choosing hard or soft edges affects the focus of the painting.