Grass is a timeless pixel art topic. The almighty grass tile.
Two very quick thoughts:
1. The macro shape of the land is carved out by the grass. The overall land has it's own shape and is carved and lit as its own large object.
2. What you've got on your's is a dark background with some darker color strands.
What I would suggest is the ground is actually darker, because less light makes it through the grass cover.
Instead, each strand of grass , and patches are lit up as their own thing.
Some strands of grass are burried deeper while other strands overlap them.
Here's roughly what I mean:
Hope this helps breathe some life into your grass!