If you are at a gate, and have the default "join existing party" settings, then instead of randomly being assigned to a party or to a new group, how about displaying all of the parties with your friends, and then all (some?) of the other parties that you are eligible to join.
Along with this, an indication of "how old" that level is -- so you know if you are joining an early level or a late level.
Right now, it really isn't clear. I just saw at firefly that I had a friend in the dungeon -- so I tried to join, only to wind up on the party formation level.
We already have that option - click the "Join Friends" tab in the Adventure Board.