I like the shapes of your grass leaves!
I'm pretty new to this myself, but I'd say you probably want to increase the dynamic range of the palette. Get some brighter greens in there, and some darker greens. Same for the stone.
With some darker greens you can start to place shadows under the leaves. This will make them pop out and look more 3D. With a brighter green you can add some points of highlight to emphasize the angle of the light source and give the leaves more substance.
I have a couple of questions:
- What angle are we looking at this from? Directly above? At a 45 degree angle to the ground in the traditional RPG style?
- Where's the light coming from?
Also, do you want to talk about the stone tile?