In Mass Effect 3 for the PC, PS3, and Xbox 360, you can unlock characters, weapons, mods, etc. by purchasing card packs which require credits.
You have two options to get credits in multiplayer games. You can use your hard earned real money to buy them, or you can earn them by successfully completing multiplayer games.
Bronze Match – These are the easiest matches, and completing a bronze match will net you around 15,000 credits depending on how quickly you complete the objectives
Silver Match – These are the middle tier matches, and completing these will net you around 30,000 credits
Gold Match – These are the hardest matches, not for the light of heart. You’ll probably want a team of good players, higher level characters, and better weapons unlocked for this one. These will net you 60,000 points or more though if you can complete them.
Tips to Maximize Your Credits
One common mistake that a lot of people make is to play in matches they’re not prepared for. If you can’t complete Gold matches, then don’t attempt them because you’ll be wasting not only your time, but other people’s time as well. That half hour you just wasted getting no points failing on a Gold match could have earned you 30,000 points instead beating a  Silver match. Don’t be greedy, play the match you’re ready for.
Try to get a team of people to play with. Even if you don’t have friends playing the game online, try to friend the people you play with in random groups that are good players.
If you’re playing in random matches, choose a strong class like an Infiltrator instead of a support class. Let’s face it, randoms are the worst groups for cooperation, so you’re going to need every advantage you can get to complete matches successfully.
