Hi

This is a really neat artwork.You are still young but have a good sence for a nice motive.
The motive is really nice and also the perspective of the picture is really good but it could have a bit more space around the girl.
Also you made a good effect of deepness with the grass, let it become blury in the background is a good way to bring deepness in the picture, well done!
Next time if you draw grass maybe you try a brush with more random strokes, so it would look more natural.
You also tried to give the picture an special atmosphere with the light, this is a great idea and the sunray´s are used in a good way but cause you´ve used a small canvas it looks a bit like the girl is sitting in front of the sun. So again I have to say, work on a bigger canvas..
So now to the character itself, the proportions are not bad but the anatomy needs still work. Maybe you try to do some body-study to learn about the human anatomy, that can be a big help to learn how which muscle should look <img src="e.deviantart.net/emoticons/s/s…" width="15" height="15" alt="" title=" (Smile)"/> Right now the body looks a bit clumsy.
On the pic the girl is waving with her hand.. it looks a bit like she has 3 right arms.. with a lower opacity you can get a better waving-effect and give them a good contrast to the real arm.
You still have a hard row to hoe but if you keep on working it will become better.