Alright, now I've never really done this before. So bear with me here.

Background:
The first thing I'd like to point out is that the moon isn't a floating gray ball. It has details in it that can be seen from a distance. Such as craters. I recommend Googling images of the Moon and studying them.

Second thing that I noticed was that the sky is pitch black. Literally! Usually the night sky is a very dark blue. Not ink black. The stars also look very out of place. The dots used should be a bit smaller and more spread out. There should also be more of them in the sky.

Now for the ground. If it's supposed to be night time, the ground itself should be a lot darker. It just doesn't look right if the sky is dark, yet the ground is bright and vivid.

If you're using Photoshop, there are ways to make the ground match the sky. You can hit CTRL+U and darken the ground layer, or make a new layer over just the ground, color it black, then set the opacity of the layer to 50%.

Another thing about the ground that kinda bothers me is that there's hardly any detail to it and that it's just a gradient. I can't tell if she's standing on a rocky surface or sand. It's usually a good idea to detail the ground as well. That way, people can get a better idea of where the character is.

Character:
I'll start with the anatomy. First thing that caught my eye was the way she's standing. Her hips seem to be angled way too far forward from where her legs touch the ground. This can be fixed by moving the legs farther forward or making her lean less.

Another thing about her body that caught my eye was that it looks like she has no natural curve to her waist and no hips. Generally, female characters have a vase-like curve to their bodies. I recommend looking at some tutorials so you can better understand what I mean.

Also, her feet don't look right bending in that way. Considering how her legs are positioned. If you were trying to make the right foot (foot seen on the left) face the viewer, you don't need to include the shoe's heel. It would normally be hidden from view. Her arms are too short as well. The hand should be down by the bottom part of her skirt.

Okay, now for the coloring. I see you've chosen gradients for the shading portion as well. This really isn't a great idea if you don't add proper shadows and highlights to accent the coloring. It looks sloppy and kinda rushed to me. Plus, the light source is inconsistent. The pants and the character's face's light sources contradict each other and that's usually a bad thing.

A good way to make sure your shading is consistent, is to draw a small red (any color would do really) dot at the top left or top right corner of the page and use that as a reference of where the shadows and highlights go on the character's body. Trust me, it really helps.

Overall, this isn't a bad piece. The expression on her face is fairly well done and I like the character's overall appearance. All you really need to do is keep my critique in mind and I'm sure your next drawing will come out fantastic.

Keep practicing.

I love how you used lots of gradient, this picture is cute c:

First of all, the body looks uneven. The upper part of her body (above waist) doesn't look much connected to the lower part. Also, the moon would need to have craters made on it for it to look better and more real. There also should be more stars, but if there is little stars that night, scatter them all around. Also stars come in MANY different shapes. I suggest to use the soft brush if your using photoshop or a program like photoshop to make the stars.

Hope this helps you, great job overall c: