asked me for critique. The picture on the left is theirs, and while looking at it, I realized that often my backgrounds have similar mistakes, since I'm not yet good at them either. So I decided to put this here to help all of us figure it out. 0u0
First of all, these clouds are cool, though I'd give them more cartoony look to match the trees. Sky colors are nice, too.
The trees are cute, but if they're all similar, it gets boring. Make some trees shorter or thicker, bend them, play with the crown.
The most noticeable thing here is perspective: you see there's quite a distance between the red and the yellow ones, and yet the yellow seems even BIGGER (sure that's possible if in fact it's much more larger than the red tree, but looks weird anyway) Moreover, don't forget that the futher objects are from us, the more transparent they become, so the purple tree is too vivid.
The landscape may seem to be kind of deserted, because everything you can see is bare soil and trees. Add grass, bushes, flowers, more trees, birds, butterflies, forest in the distance, small town, whatever is your purpose!
As for colors: try not to use black for shadows, especially when you have such bright light. Plus, remember that when light is warm (yellow), shadows are cold (blue) and vice versa.
The right picture is how I would draw that landscape, considering everything stated above. I guess I learned something useful today 8D