There's a current thread on the steps of mapmaking, with references to other such threads.

Welcome to the Guild! Yup, it could take years to get really good, BUT those can be quite enjoyable hours and hours, and intermediate maps made can be perfectly useable, pleasant, and pretty. And enjoyable. Did I say enjoyable? For y'see - if you dive in the time span becomes "in mere hours you can be better than you were" :-). Quickest way to improve is to jump in and start a Work-in-Progress thread, and ask questions as you go. We're a gentle audience. I have a river cop's badge, for instance, but no nightstick :-).