Well, the very first thing I would do would be to get rid of that strange boxy gradient around the moon. You should do something more purposeful there, something that doesn't detract from the beauty of the moon. There's a lot of stray pixels especially in the sprite that's adding noise to everything. It makes it hard for the eye to rest anywhere and on the sprite it makes the character less readable. You do a pretty good job using shadow to define form, but for some reason your highlights aren't doing that, they seem much more randomly placed. The pallet needs the most attention, it looks very haphazard. Think about what color the light is, how that would effect the hue of the highlights or shadows. Think about how contrast and hue determine where your eye naturally goes in the image and how you can use it to highlight the things of importance and lead the eye. With such a bright moon I would expect to see more highlights. You could use it to define the walkable areas better.
Your tree isn't too bad, I think if you clean it up the same way I suggested for the rest of it you'll see some improvement, especially if you do more purposeful and form defining highlights. You might want to make it less lopsided too.