This can be done in two ways:
1. Create your own club, go to Xbox Live > EA Sports Hockey League > Create Club. Set up your club, then go to "Invites Sent" and press X to invite friends.
2. Join the "x360a" Team by requesting to be added in the "Official MMO League Thread." It's a team set up primarily to boost the online league achievements.
Either way, go to the Dressing Room, as soon as 2 people are in the dressing room you can play a game. Finish the game and the achievement will unlock.
The server for this game is now closed and this achievement is no longer obtainable.