I want to begin by saying that I love the feel and the palette of this set.
That said, my personal advice here is as follows:
Less is more when it comes to suggesting grass and dirt. The grass's level of detail and personality is very dense compared to the dirt next to it. I think you're trying to pack way too much visual information into each tile in an attempt to make it more "real". You may either want to:
1) reduce the contrast between lit and dull grass sections to make it smoother, as well as adding more texture to the dirt to make it equally visually interesting
OR
2) Simplify the grass or change it to a more suggestive design so that it is no longer being "framed" by the dirt like it is in your current scene.
Here is an example of each:
This is Seiken Densetsu 3, one of the games that many a pixel artist feels represents the ideal in lush tile-based worlds. Note they have a very dense grass pattern but they keep the shades closer to each other so that the eye slides easily over the detail where yours is such a bright/dark contrast that it urges the eye to stop and examine the details.
This is Mother 3 and it attempts the exact opposite : incredibly simplified tiles that use darker green grass blade symbols sprinkled into the light green to suggest the presence of grass. You know grass looks nothing like that, but it's so simplified that we accept it as a symbol and it helps us focus on the characters within the scene.
Your grass currently is closer to Seiken Densetsu 3 while your dirt is closer to Mother 3.
Hope that helps,
Great work and good luck!
