Quick! Here’s the homework, so you can go out in this sunshine and look at shadows.
Find a sunlit surface, like a tree trunk, or a dog house, with shadow on part of it, and which casts a shadow on another surface (the ground, a sleeping dog).
How much darker is the shadow area?
How does the color change?
What kind of edge does the shadow have?
When you have the answers to all the questions, you should be able to apply the paint very confidently and efficiently. To practice getting it “right” on the first try, resolve not to correct any of your attempts. Instead, take note of what needs to be changed and paint another version.
Use a piece of practice paper to try out color, edges and value. When you make the overall wash for the local color (the sunlit surface), make a large patch of it on the practice sheet, too. Then you can test your shadows there and see for sure whether they satisfy you.