The mage is cool! You really applied what your learned from Ryu's edit
. Tiles, what curly said above. Let me try to help a bit:
Before texturing anything you should try to have very distinct shades to represent vertical planes (darker walls), horizontal planes (floors) and inclined planes (ramps/stairs). If light comes generaly from above, walls should be darker, floors should be lighter (because they are facing the light more directly), and ramps should be somewhat in between. Of course, when detailing a scene not everything will be made of the same material, and some materials are inherently darker regardless of shading (dark stone vs bright stone in your case) but first get the basic values straight, then variate latter.
So what I am suggesting is that, at first, you try to draw the scene with mostly flat color tiles, maybe just some outlining, to get a feel of the 3d shape of the scene. If you have trouble defining a scene with very flat shaded tiles, then the texturing will only make it harder. Chances are that you will spot some geometry mistakes that you were not noticing before because of the distractions.
After that you can start to cast the shadows on the floor, and then texture over the values that already give an idea of the basic 3d solids the scene is made of. As a rule of thumb, the texturing should be less detailed than the characters, so they stand out over the tiles.
