I RP in the Reygarth thread. I occasionally get a request for a DM RP, but my favorites are the ones who looked over my characters there and said "ooh, I want to RP with her or him" and then message me about it. Public RP ain't for everyone, but it's gotten me some incredible RP partners.
The best ones I like are the requests related to one of my comments. ^_^
Whether it's a compliment to one of my comments that eventually leads to an rp or when someone decides to send me a nice rp starter based on said comment!
Decent grammar, and not jumping straight into the sex. Being able to talk about what we both want is important! Kinks, limits, story (if any), all of that makes a good RP. Without it, knowing what will really get your partner riled up is difficult.