Search for a player or players over Xbox live, it must be ranked, no skirmish offline. It can be done in any playlist online. Depending on how good you are you should either play 3v3 standard for people who have just started or 2v2 deathmatch for people who can play deathmatch. At the very end of the game after the bonus multiplyers have been added, the person with the highest score gets the achievment, but they might not win the actuall game, this is down to the bonus multiplier. I.e.- Player 1 scores 306 and gets a bonus multiplier of 3.5 which equals 1071, but player 2 scores 297 with a bonus multiplier of 7.9 which equals 2346, player 1 might have won the game but player 2 got more points and the achievment.