I'm hypnotized... First, it's good how you joined all parts to make moving picture- there's background with various buildings, there's wall and there's sidewalk with dude on it - picture has volume. Now we need to improve the parts it consists of. There are obvious problems with dude's proportions - any basic anatomy tutorial will be better gude than me - so use it. With comic characters some stylistic questions will arise, so my advise would be to steal from everywhere and use what you found in your pics while maintaining certain level of creativity to not make rip offs and edits. You used dithering and shading at some places but it's useless because 1) tones not far away from one another, so effect is lost when looking at 1x 2) shadows come from different lightsources. Also don't be afraid to experiment with palette.