This is fairly straightforward, and I don't think it's really necessary to list tactics for each game type.
Usually, you can do this by playing against only one CPU opponent, set to easy, with a 1 minute round time. Be quick off the blocks to either capture/kill/claim whatever your game type requires and you should be in the lead once the timer expires.
The exception to this rule is the Rocket Race game type as you cannot set a timer for Rocket Race games. Sometimes, having two easy opponents, letting them fight and eventually weaken each other will allow you to swoop in and claim victory.
Alternatively, you can boost this easily with a partner over XBox Live.