a good way to help your image is to draw single bold strokes, you can sketch out your idea then tone down the opacity in photoshop and try to use less strokes to get the information across this makes for more confident line drawing and will really help clean up your image and teach you how to express the same information but with allot less noise.
Don't rush, take your time with things and keep drawing the more you do and the more you make yourself finish the more things will begin to settle.
Also always define a light source before you start this really helps give believability and life to your images and helps with rendering also.
I'm really pleased to see a good mix of characters and environments here and i think your on a good base to sky rocket ahead! keep going