There is something calming about painting skies. It's one of my favorite stages of a painting. The most important tip on painting them correctly is to keep their value a little darker than the sky itself. Another thing you need to be careful with is the edges, if they don't look right to you, then you might want to soften the edges. In this video, I'm working on semi dry layer and the edges are hard, so I will go later and soften them when I work on the tree branches. Let me know what you think. Good luck with your art!