We just went through the exact same thing, after months of "being on the fence", nervousness and hesitation... so what happened with us is we found an interracial couple to play with, they are really good with newbies and the wife made my girl really comfortable and relaxed about the whole thing, so I would recommend a couple to start with..
In terms of what to expect, it was still super nerve-wracking and weird seeing your wife with another guy, but it was also incredibly hot!
So the way it worked for us, we met them in person for drinks and dancing the first time, had a few drinks, some close dancing, light touching that slowly got heavier towards the end of the night...
Our second outing we had a hotel room, we had tentatively agreed if the vibe is right to do a "soft swap" (just things like bjs and handjobs) with the potential of going "full swap" if the mood strikes... needless to say, we were "full swapping" balls deep 15 minutes in lol...
Not saying that's the only way, just saying it worked great for us
