Good way to improve writing skills?

It's not as though I'm a complete idiot, I am actually pretty intelligent. I'm an avid reader, so writing should come easy, right? What are some techniques to improve my writing skills? For some reason my writing is always chaotic. I can't seem to formulate anything properly. My writing usually jumps around too much. It's especially hard to stay focused on ONE, main, point. I have a tendency to veer off topic much of the time. Any suggestions would be greatly appreciated, thank you!