Read some tutorials in the terrain tutorials section. They would help a lot. Also look at some other peoples work... maybe mine?! lol
You need to add height variation. Take the raise ground tool, put it to the 3rd size, and click a few times in a spot to make a small bump, make more all over, you'll get better the more you do it. Do not use the noise tool. It is the worst tool in WE. Now use different grass tiles (You may need to add some, go to modify - modify tileset) and use them all around, this gives tile variation which helps a lot. Next take the shrub doodad in environment and add it amongst the trees. You can look around for more plant and decorative doodads and add them as well. Then you will have a decent terrain!