I'm pretty terrible at pixel art; however, I have been focusing on the elusive grass tile for months and have finally figured out a passable method of creating them on a 16 x 16 scale. You need 4 different shades of green. Colour the entire 16 x 16 box in the darkest green. use the next brightest green to paint curved lines 1 pixel thick and about 5-8 pixels long. I tend to use a 3 by 2 by 1 method. Make sure non of the lines touch each other and try not to put the bottom of the grass blades in the same line or else it looks funny. Once the lines are drawn, add the brightest green to the tops and the last shade of green (one shade darker than the brightest) below the brightest green on the grass blade.

I attached an example for you to this post. Hope this helps.