Everything you write makes you better. But if you really need a tip, here's one: a good story begins in opposition to its ending. That means you work out how it finishes first, and then begin the story as far away from that point - in terms of character development - as you can.
I do screen work, adult books, kids books and comic stuff, which gives me a pretty full plate. The problem is usually choosing which one I want to work on next.
I like writing comic pages, discovering the rhythm of the panels, learning how much you can and can't express. It's good to stretch myself as a writer instead of always doing prose work; I write screenplays for the same reason.