You'll have to complete appropriate achievement to get the allotted gamerscore.
Imperial Instincts - Earn 25 cumulative point captures in Conquest.
NCC-1701 - Earn 250,000 points as the Flagship class in one Team Deathmatch game.
Starfleet Medal of Honor - No deaths or ejections, plus at least 15 kills, in a single match.
Vulcan Wisdom - Don't die or shoot, yet capture 3 points (including the enemy base) in a Conquest match.
Academy Graduate - Earn 1 kill with each ship class.
Born Leader - Capture 3 points and help destroy the 4th in a single Assault match.
Bridge Commander - Earn 250 cumulative kills in Team Deathmatch.
No Mercy - Earn 50 cumulative Escape Pod kills.
Red Shirt - Be the first to die in a Versus multiplayer match.
Dreadnought - Destroy all 5 ship classes plus and 1 escape pod using the Missile Cruiser.
Kobayashi Maru - Some achievements are unachievable... unless you cheat.
Mirror, Mirror - Capture a point with the aid of your own wingman.
Captain on the Bridge - Earn the Captain rank in Survival Mode.
Nero's Rage - Destroy 3 enemies while using a single invulnerability powerup.