Good:
- It tiles rather well. Nice job on that!
- The color base shade is a nice choice of green; not too bright, not too dismal.
What needs to be improved:
- You might want to double the amount of grass strands in the tile; it looks very bare right now, as if there's a green carpet and a few strands are coming out of it.
- You'll also want to add a little more contrast between the brighter two shades and the darker one. That way you'll get better grass blade readability.
- You might also want to consider straightening out the blades a bit to make them more erect in posture; then it's also easier to fill in the space with more blades as well.
- Finally, you might want to let up on the brightest color there, some; with so few blades, it dominates the middle green color. However, this might get fixed automatically by adding more blades and straightening them, so I wouldn't worry about this until you make the other fixes.
Not bad at all for a very beginner pixel artist! Much more impressive than my first grass tile (or even, first few months of attempted grass tiles...)