Mathias is right in his flat statement. You need to apply your shading more volumetrically and try and apply form and shape before applying texture. I'll admit, it's sometimes hard to do, but in the end it'll look better.
You need to also set a lightsource and figure out where the light is coming from. Right now, on the stem, it looks as if it's coming from both directions, whereas on the cap it looks like it's coming from the left.
With this new screenshot, it seems as if you're going for a top down look, which the mushroom gave no indication of. You seem to have the same lightsource problem on the rocky cliff as well. It seems flat and doesn't have the rocky feeling one would expect from a cliff. The styles also clash- the mushroom has harsh, dark outlines, whereas the cliff seems to have lighter, soft outlines, and in some places, no outlines at all! I think you need to give the mushroom more shape and give it a more top-down appearance. It would also help to add some more volume onto the cliffs and try and apply a rocky texture.
Your grass tiles aren't bad, but I think they could use some differentiating. You can see lines in the patter in which one line of grass tiles meets another. If you made 3 or 4 individual, yet tileable, tiles, I think you could make the grass much more interesting! Also, try and throw in some flowers and such. Visual interest is quite important.
Anyways, looking forward to progress, I think you have it in you to make this a really nice pic. Good luck!~