I think i started with a river, they're easy for beginners.
Anyway, a few tips:
1) Try to use better tile variation, solid grass doesn't look good when it's everywhere!
2) Use the smooth tool on the sides of the river, it's really rough.
3) Grass doesn't grow under water, throw a rock tile under it.
4) Never show the end of the map, it just doesn't look good.
5) Please crop your pictures.
It's ok, for a first terrain.