Darn, Kazayu beat me to it. I'll probably go ahead and do it anyway to see if we coincide. We'll see what I can come up with.
Or not maybe. In the edit I've made, (trying to make it myself understandable) I've broken up the edges of the river like Kazuya said to. I think your moving in the right direction with that ledge piece there. But remember you need to cover all the sides and corners to make it readable. (Yes, I know your going to do that.) Also, that ledge of grass would only work in that situation. It needs to be moved closer to the edge a bit. Also, with the rock edges, they need to be broken up as well. I was going to show something else but I wasn't sure of (if any) your restrictions on the piece.
Oh, your colors confused me a bit. I thought that the foreground was supposed to be lighter then the background right? And, that taller things were more brighter up at the, uh, top. I also think you need to change the water color. I couldn't tell what was water and what was holding places. (Other then what was obvious that is.) Oh yeah, with the cliff edges. Those, sides appear to be jutting out seperatlely away from the cliff edge. Like they're pillars. Try using some of the same brown colors of your house there. I was going to say a few more things, like about the cliff side bottom color and texturing the grass tile some. But I think I'll let others say it.
Also, this looks a bit like the GBA style. You might get some extra help looking at the Fire Emblem and The Sacred Stones tile set.
(Your probably wondering what business I have trying to help You in this area. Well, the thing is, I like doing map pieces. Give me a map editor and I'll make a bunch of maps. I may even try to edit some and make my own tiles as well. So, I know a few things about game maps and wanted to see if I could help you out any.)
(I probably should've waited for Kazuya's edit though. To me, I seem a bit harsh and could probably give myself that advice. Sorry if I offend you though, great, now I feel like a stuck up and idiot.)