1) The screentone is super green. I suggest toning it down a bunch.
2) I personally think you should expand your river a tile or two to make it look like a stream. Rivera and streams are not that short.
3) Add more curves to your long grass.
4) I have learned that using undulations like that in my opinion looks bad.
This makes undulations look a lot better. It doesn't have to be sand, but something that would make sense.
5) You seem to clump the same type of objects together. Spread them out.
6) Objects such as those piles of rocks make no sense. There are no cliffs or rocky surfaces, therefore there wouldn't be any rubble.
7) Just like the river, the path should be expanded. Remember, that is a path that is eroded in time or a dusty trail that has been forgotten. It naturally would be bigger.
8) Weeds look better if you clump the one and two weed tiles together and can really add to a map.
9) Those clumps of grass should be used on the sides of the long grass tiles, not out in the open. The big, round one is acceptable but the thin one just looks bad overall.
10) You can use a variation of trees that add life to your map.
11) Some areas are desolate. Add some more plant life to the places that overall have no plants, just trees.
12) Get rid of the pink flower. You had a nice palette of the while and yellow, adding a pink kinda ruins the feel altogether. You are trying to create a mood and the less colors you uses, the more precise the mood is.