Well, there are two factors that have affected the quality of my comics. The first is just effort. I spit out the first 20 comics in 10 days, and really wasn't putting as much effort into them as I do now. Interestingly, the first comic that I really tried to make look good was the one titled "Effort." I decided it was about time I made cells, and put a background in.
The second factor is just me finding shortcuts and easier ways to draw certain things. I don't really feel like any of my motor skills have really improved. You can only get better at this with practice. I think almost anyone, given enough effort can draw anything. Practice just shortens the time it takes to do each step. As time goes on as well, you discover better ways to do things, which are often more difficult, and can often take longer. So just practice