Ok well, first off I think you have a pretty unique style going on here. this is a very nice piece. the composition is well done. Your style is very graphic and illustrative. Graphic and Illustrative is something I know a little about. I do see a few technical difficulty but with any new style you will probably work them out as time goes on. the thing is, not to change this piece but to go on to something new and continue to improve. This type of style lends it's self well to tattoo art, ads, pop art, surrealism this type of stuff.
Now as far as where your posting art, I personally would never post my art on Instagram. As far as deviant art go's, well as with any forum goes, you get out of what you put into it. I have an account over there. One thing to remember over there is that most of the members over there are heavily into concept art and anime.
Anyway I'm looking forward to seeing more of your art.