I would gladly help, but I'm a bit in a hurry now. Actually, your work isn't that bad, but it surely could be made better if you know the little tricks of graphic illustration and by exercising your spatial vision and your grip (these last two can only be done by drawing a lot). Ideally, you also get to learn the little tricks by trying to draw something and failing horribly. Then, next time you see a photo/picture depicting what you tried to draw you'll know where you have to look.
Knowing where to look in a painting also requires a bit of training, but it's the most useful trait you could acquire in this field.
The background would had looked better if proper perspective had been layed before drawing, but in graphic adventures it's not that important because sprites don't move according to perspective, either. One "trick" that helps defining distances is to use a lighter palette for distant objects. The more distant, the paler the colors. Right now, your picture looks as if everything were equally closer, except the tree.
The color of the foliage also can look better if you don't surround all the borders in black. If you look at the tutorial, the side from which the "light source" strikes has no shadows. You only get shadows around all the surface if the "light source" is inside the leaves.
Finally, when you do those "big strokes" before blurring the surfaces, you have to apply the strong yellows and whites in the parts where the light would illuminate the surface. Think of pyramids, spheres and planes. This requires a bit of practice, because if you put the lights wrong it will look very weird. Sometimes I have to fix them afterwards because I put them backwards.
Hope these small directions help you.
