Well, I'm no Photosoup expert by any means, but I'll give it a try. Mind you, I think it doesn't look bad at all!
First of all, you'll want to change the order of the layers, since now you have the trunks of the trees overlapping a mountaintop (lower left corner). Secondly, maybe a texture underneath the forest would look good. I'm sure the tutorial/resource section can provide you with some eye candy I really like the colour you've chosen and the paper shines through really nicely.