Was quite surprised to see there was no guide for this. This is predominantly a guide to boosting it.
You will need 1 boosting partner, there is no need for more people. Now wiith the grand slam achievement if you were the first two people in the lobby you would get paired up. With the quick matches this is not the case.
You are matched up based on your GRADE. So what you need to do is alternate match wins with your boosting partner, otherwise after 3 or 4 wins you will no longer get paired up with your partner. I did this with my wife last night when there were about 50 players playing quick matches and we always got paired together unless one us of joined a lobby which got filled straight away or the timer was less than 2 seconds.
When searching, make sure one of you searches a few seconds after the other because if you search at the same time you will automatically be put in separate lobbies.
I found that upgrading your player is a good idea incase you do play randoms, as most of them suck, they just have good stats.
Finally, you CAN just forfeit the match as soon as it starts, playing them legit does not change the amount of grade you earn.