Well, I have my own experience with RP, and when I decide to do something.
I always just... Get an idea, or concept I really like, which never really leaves my head until I put it on paper. At that stage, I just have this creativity and a ‘push’, which propels me further to make it bigger, and turn it in a story.
I have this every now and then, and the only reason why I joined RP, is to tell the story to others, and thus my recent faction is born.
Im currently working on a comic as well, but since Im moving houses, it is delayed.