Candy Man is right. Think about pulling up references of tree trunks to get a feel of what they really look like. Same goes for the leaves and grass. Which, by the way have little to no sense of light.
The composition of the scene is really off. You've got little Red Riding Hood off to the right, the Wolf to the far left, then you've got this huge tree in the center, whose canopy boldly pushes right through the borders of the scene and leads the viewer's eye up and out of it. By pushing them off to the borders of the scene, making the tree twice as large and bright as either of them, you're making it the priority of the scene. Well, to be fair, Red's a bit more saturated than her surroundings, tree included, but then that means she's more saturated than the entire scene (the entire scene was pretty saturated to start with). This does draw attention to her, but considering her size and position, the eye doesn't have much to go around; the fact that she's in the corner, or her stiff and oddly stark position much like the wolf's, doesn't help. This isn't the best choice.
A lack of understanding of perspective probably causes half the faults in this piece. The other half are caused by a lack of understanding of your lightsource, atmosphere, contrast, saturation... The list goes on. Ask yourself these questions: What time of day is it? This isn't very apparent in the piece. The bright tree and Red Riding Hood suggest exposure to sunlight, but layers of trees recede to a darker color in the background to suggest nighttime. What's the kind of atmosphere you want to give off? Eerie, like you're being hunted or watched? I think that's what you wanted to do, but you ended up making all the mistakes I've listed so far. Where is the lightsource? Upper left, upper right, frontal? Right now it's very inconsistent.
That must mean... this calls for a
R-R-R-R-R-REDO
Coming soon. Dpixel's edit of the wolf is in the right direction in terms of lighting, though.