First of all, I absolutely love the choice for the background design. The galactic look is vast and intriguing and definitely helps to draw attention to Hinoka. The colours in the sky also look somewhat like the northern lights which I personally enjoy. What I might suggest for future galactic-styled pieces, however, would be perhaps a little more variation in the light coming from the stars. Stars don't all tend to glow the same colours or even at the same intensity as shown here. In adding a few brighter stars, perhaps some shining with a more blueish or yellowish light the background will be a little more involved but won't at all take away from Hinoka's presence as a character.
Anatomically and based on Hinoka's stance it looks as though you were going for a slightly low angle perspective (based on how much of the underside of the character's chin is visible. It's a very nice attempt but based on the angle you chose the shoulders should probably be raised higher and therein closer to her chin. The farther down you look up at a character from, the closer together all of their vertical body parts become.
As an example, press the tip of your index finger to the screen. Looking straight ahead, match the bottom of your finger to the top of Hinoka's shoulder. The top of your finger is about as high as her shoulders should be for the angle you're going for.
Additionally, there should probably be more space between her chin and her mouth (since you can see under her chin). This creates the illusion that the viewer is not only looking at her from a low angle, but also that she's looking down at the viewer from above--which might play very nicely into the galactic-styled background.
As I understand it based on your other images of Hinoka (in your gallery) the long purple sleeve is meant to be connected to a second shirt under the black one? (Is that correct?) If so, the long sleeve for that shirt should probably be placed a little bit higher on her arm. As it is now, it's so far down that it should actually be pulling down on the arm opening for the black shirt.
With regards to the character's hair there seems to be little consistency in the patches of red hair with relation to the predominantly brown hair. It's perhaps a little too evident that these red patches were added exclusively digitally and with little guide where they would stop and start. For future pieces I would recommend drawing out more individual strands and swaths of hair when sketching the piece. Not only will this add a lot more depth and involvement with the hair itself, it will create very obvious separations between the red and brown strands of hair.
On a related note, I enjoy the darker tone you've used for Hinoka's skin across the board (really making it feel as though we're seeing her at night or under low light) but there are a few inconsistencies and places where you can further build upon this. For instance, the lighting effect all around Hinoka's hair should indicate where any light sources are coming from and this should match the light sources and shadows present on the rest of her body. However, the light on Hinoka's hair indicates a dominating light source coming from in front of the character, with some more light sources shining around her head, but that implied light source doesn't present its effects anywhere else on her body or clothes. Her clothes actually have some shadows but they indicate a light source coming from the opposite direction. Similarly, the glow coming from the symbol on Hinoka's back doesn't spread onto her skin or clothes--more that it exists as a disconnected glow. You should try planning out where your light sources will be when first working on the piece so that as you work on it you can notice and correct the placement of your highlights and your shadows. Doing so will also help you to plan out more obvious and intricate shadow designs and sources of light.
A very nice attempt, especially on the background, but a little more planning in the beginning stages of the piece will show their effects tremendously as you continue through and eventually finish your future pieces.
That's all the critique I can offer up at the moment.
Hope it was helpful~