The Royal Sniper is really neatly designed. The colors you’ve chosen go well together. I’m not an expert on poses but what I can suggest is shading. In the “backgrounds” tab there is a gradient circle under “shapes”. If you make the line and outer edge of the circle completely transparent you can use the middle part for highlights, shadows, glare, all sorts of cool effects. It can really bring depth and realism to your pictures. If you check out my thread you can see some examples of how I use it.
Backgrounds also really help improve a picture. There’s also in the same tab a gradient rectangle that can make beautiful skies. Try layering different background pieces to make fuller scenes.
My last suggestion if you want to try a more realistic style would be to color the outlines. Leaving them black give your images the classic “comic book” appearance.