I agree to some point with Souly. You need to work more from generic to specific. Do your lines, they can be sketchy, as they will be pixelled over anyway (I for my part see no need whatsoever in doing superclean lines, I only do it when I do geometrical stuff that needs construction). Once you have a decent sketch, think about how many colours you wanna use and make some ramps that suit your needs ok. Then block in your colours, THEN detail such as dither and aa. I don't do this myself all the time, but it is good practise in general.