FanFiction.net is the world's largest fan fiction archive and forum where fanfic writers and readers around the globe gather to share their passion.
This article on wikiHow goes through a step-by-step process on how to write a fanfiction.
How Fan Fiction Can Improve Your Writing This article has been written by Colleen Mitchell for The Writing Cooperative and discusses how to start out writing and why Fan Fiction breeds creativity.
6 Ways That Fan Fiction Makes Your Writing Stronger Written for tor.com, Vivian Shaw shares her top six points from writing Fan Fiction that can be applied to writing of any style.