Welcome to Wyrmrest Accord!
As people have pointed out, the Valley of Honor in Orgrimmar, the Mage Quarter in Stormwind, and almost anywhere in Silvermoon are full of people idling about, waiting for walk ups. There’s also social RP events, like the Stranglethorn Bash going on this weekend.
And tomorrow…
And the day after that…
And after THAT…
And that’s really just some of it. There’s lots of guilds hosting stuff. It doesn’t tend to get advertised as much server-wide, even if it is open to the general public. My own guild has one such event tonight.
I’d also recommend checking out Tumblr and the various Discord servers where people regularly post public events.
Basically, be open and honest about the kind of RP you’re looking for (action, adventure, romance, intrigue, horror, etc) and keep hanging out with people in walk-ups. I suggest trying to come up with a hook, like being a character looking for work of some kind, or looking to help people in a particular area. Eventually you’ll meet characters/players/guilds you click with.