From Halopedia, the Halo wiki
Send half to Southern Release area and half to Northern Release area. Put Spartans on the Release Controls.
Release the Flood periodically. There is a cooldown period between each release. Keep doing so until you get 4000 points and then attack enemy base.
Don't activate any skulls and remember that the enemy will sometimes attack your base.
Max points actually became 4000 per game due to a Title Upate.