Sketchhhh

Interesting sketch. Who is this girl? :'D

My first advice is to draw poses/anatomy from reference. Her proportions and anatomy are very off. Her right arm is placed very awkwardly and is shorter than her left arm. o_o You really need to think about the structure of the human body and place the eyes in the sockets, plan the pose along where the bones and muscles are, etc. Don't just think about how it looks on the outside - think about the inside. Don't just draw a person, but discover a person every time you draw. Thinking about what you are doing and why it is the way it is helps a lot. Draw from life. Draw from photos. Just familiarize yourself with the human body as much as you can. Also her left hand is backwards.

The folds on her shirt are good, but her skirt is off. As someone who has sewn quite a few of them, I can say that pleats don't quite hang like that. Look up photos of pleated skirts and figure out how it would hand, crease, and fold off of the shape of her body.

The background is cute, but it looks very lazy/rushed. Honestly, it's sometimes better to leave a simple two-tone or gradient background than to throw in something quick and sloppy. Backgrounds are one of those things you either go all out on or don't do at all, really.

I hope this helps!