To unlock this trophy you must be at least level 18 in game, There are 10 different Counselors you'll need to play as. You need to make sure you finish a match whether you win or lose. If the host leaves or you get kicked or disconnected it will not count.
The Counselors are unlocked as follows.
Chad Kensington - Unlocked from Start
Jenny Myers - Unlocked from Start
Kenny Riedell - Unlocked from Start
Vanessa Jones - Unlocked from Start
A.J. Mason - Level 4
Deborah Kim - Level 6
Brandon "Buggzy" Wilson - Level 8
Eric "J.R." LaChappa - Level 10
Adam Palomino - Level 14
Tiffany Cox - Level 18
There is also 3 other Counselors, Mitch Floyd (Level 24), Fox (Level 32), and Sheldon Finkelstein but they were added in free DLC and are not needed for the trophy.