As a newbie who has attempted twice to initiate an RP, do wait. Like the others said, join a few RPs, make sure you build some good relationships with other participants and pay attention to how good GMs handle certain things. You can learn a lot.

If you can't wait, you can go the easy route and lure the majority with an RP concept that you're sure will reel in a lot of people ([b]read:[/b] popular fandoms, multiverse, crossover, high school), however chances are they won't last long. That's because they mostly attract people that have no issue with hopping from one RP to another when their interest begins to flicker.