Another way to get into RP, if you are not ready to get into a guild is to go to events. There are many communities and projects for doing so. If you don’t mind RPing between alliance and horde characters, you could check out things Free Seas puts on.
You will want to stock up on Elixir of Tongues that are sold in Dalaran.
But the other thing I want to point out is you don’t need a backstory to get started. I have RPed Persefani for coughs 18 coughs years as of December 5th and she didn’t even have a backstory until a couple years ago. While “I don’t remember” amenisa story can be seen as tacky you could always just not want to talk about it. “The past is in the past” and change the story to your character’s current state and future goals. Which, after all, is what we are RPing for anyways. Right? Character growth. (Little louder for the people in the back.)