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It's hard to provide real crits on this because I'm not really sure which bits are incomplete and which bits are finished...

i'm curious to know what program you're using for this piece. i think it'd be best to try and utilize layers, so then you can color areas like the skin and have it be underneath the hair so you don't have negative space between every object (like where the bangs and forehead meet i can see part of the sky). i would also try and use a hard brush to get the main form and shadows down before using a softer brush. using only the airbrush like that gives you very vague and ambiguous shading and form, and it looks smudgy and blurred. a good middle ground would be to use both hard and soft shadows, but even hard shadows are better than overall soft ones unless the lighting calls for it (like a cloudy day or something).

i think that you should work from general to specific, so the details and objects are cohesive with one another. right now it feels that everything is vying for attention and it makes your illustration look very cluttered and confusing for the viewer, especially at what you want the main focus to be. i would probably tone down all the special effects and sparkles until you're almost done with everything, so then the placement for them will make more sense. the stars look real contrasty and they're fighting with your character, especially since the main focus is so low key and blurry.

the skin is a little too contrasty and it might be good to blend in other colors to give it more life. reds and oranges are good for the lighter areas while blues and purples are good for the darker areas and shadows, with a little bit of blending from both warm and colors in where they meet. a rim light on the side that is in shadow will also help in making your character pop out from the background without making it too obvious (especially if it's opposite color of the main light, like if the main light is warm then go for a cool rim light). use other colors when you pick your hues, instead of just moving the color picker down the color square when you pick shadows and highlights.

beware of tangents (another thing that tends to happen when one doesn't work from general to specific). right now it looks like the hand(?) is emerging from the chest, not to mention it's pretty big in relation to the character. it's also touching the edge which makes for an uncomfortable composition. i would probably put more space over on the right since that's the side the character is looking, not to mention it'll give you more room to work.

the lips feel a little skewed and doesn't match up with the perspective of the face. and the shapes of the eyes feel a little too much like anime eye decals, there's no roundness or form to them. i would probably try and work out how they will be by sketching them out before trying to paint them, since you said that's where you're having a lot of trouble.