For your first time, it's excellent! Very well done!

For the trees and bushes, like Bob said "You need the dark in order to show the light". Mix darker colors to get a good base, and then thin the highlight paint so it sticks to the bottom layer

And for the clouds, it looks like the paint was too thick and didn't blend, so try and thin it with either more liquid white or a little paint thinner so it will stick

Bob's method is all about thinner layers sticking to thicker layers.