There is no best way. You join a site that cater to that lifestyle, let them know who you are, what you got and can do with it. Send some messages to let them know you're interested, and if they like what "they", not you, like, then they will initiate contact. Usually the husband and if you're lucky enough to meet then they both will decide to go further or not. The wife I find is the one to give the green light cause she's the one who had the pussy, tits, ass and mouth you might eventually be shooting your hot cum into and down her throat. Unless they give to permission to. Always respect the rules they lay down to give you the chance to fuck her.
Then all you have to do is fuck her good, make her cum hard. And impress hubby and you'll be getting plenty of invites after.