So far you recived lots of good advice !! So I dont have too much more to add ...
The wife an I have enjoyed out little threesomes and find that they bring us even closer in our relationship But we know ourselfs and Love each other BLA BLA ETc. etc. ..

And thats one of the big things you guys will need to figure out ( I suggest first ) is what is your relation ship with your GIRL ???

Now for some warnings the others didnt mention ...LOL ..

1 ARE YOU two SECURE with your self's?? no self confidence issuses ? will you/her become overly jealous is someone pleases someone else more than the other ?,Are you two stable in your sexuality DO YOU KNOW ....REAILY KNOW WHAT YOU ARE !?! etc.

2 If you get a night with 2 gals will everyone be ok when the 2 guy night comes around ? (once you start down this road LOL)!!!

3 Are you ready to HIDE the LIFE as there will be ppl you wont want to know about the turn your relationship has taken LOL ..

AND FINALY 4 ...In MOST 3somes there comes a time when the 3rd person gets old and becomes a pain in de arse ..is this a one time thing or have you 2 planed an escape route ?? ALL 3 of you need to talk this one over BEFORE YOU START ANYTHING ( Find all the hidden STRINGS etc.) Anyways im not gonna go on about STD's and safty issuse's figure all that out too and HAVE FUN!!

P.S. Lets US know when you wana try a COUPLES night !! LOL and also in some cases an adult game is a great ICE BREAKER