675,000 is the amount of experience required to reach the rank of elite. Exp is achieved by doing anything online but the quickest way to rank up quickly is to get a 4 player match of T-Hunt on any level with the settings to realistic and high population.
Of course there is also a glitch for those of us who are less adept at T-Hunting. The below video shows a fairly easy to do glitch that allows you to complete the level Countdown in about a minute. The level’s amount of experience has since been reduced to 50 exp per win but it is still a good amount of exp. What happens is that the player taps in order to take cover on the elevator and instead takes cover where the elevator would have landed. This allows the player to move to the launching pad without any enemies to fight.