Instructions
Play while connected online. All challenges in "Halo: Reach," whether they are offline or online, increase your credits.
Complete Campaign Mode, the game's story mode. Every stage in Campaign Mode gives you more credits. The higher the difficulty, the more credits you receive, so you should play in Campaign Mode on the Heroic or Legendary difficulty levels.
Battle in Rocketfight matches. Rocketfight is a deathmatch where every player has a rocket launcher with unlimited rockets. If you kill multiple people at a time, you get a lot of credits; since the rocket launchers have the potential for multiple kills at once, Rocketfight will give you more credits than playing a standard deathmatch.
Complete every online multiplayer game that you play. At the end of every multiplayer game, the players that did not quit receive a bonus for playing the whole game.
Perform career milestones. "Halo: Reach" tracks your lifetime information and credits are given to you for having high amounts of kills, like assassinations in multiplayer.