The "rules" are be self-responsible for your own stuff, and be honest and vulnerable about it. Communicate, and then communicate some more. Don't assume anything because there are no inherent rules. You have to negotiate everything with the other people involved. That's pretty much it, in a nutshell. There are poly groups in every major city, and most smaller ones. Look at Facebook, MeetUp, or just Google polyamory and your town/city. There are dozens of dating websites, but I think meeting people face to face is best.

Caveat: Not everyone who claims to be poly is doing the hard work (and it is work) to be self-responsible and honest. A lot of them are still stuck in monogamy constructs and toxic relationship paradigms. And, good people and healthy poly relationships are out there, just like in traditional dating.