Yeah I'm guessing you are skipping the summary on this one.
Have you heard of Xbox Live Rewards? If not you might want to check it out. Every month you can take a short survey (like 5 minutes max) and they offer other ways to earn Microsoft Points. The surveys are only 20 points a month, so not exactly breaking the bank.
But this month they are going big with Halo 4. The main way is by playing multiplayer. Something you were going to do anyway. At 35 hours you get 100 Microsoft points. Make it to 70 hours and you'll get 300 points. Put in 140 hours and you get 600 points. 600 Microsoft points can get you some DLC of a free game.
Sounds pretty good right? So what does it cost to join Xbox Live Rewards? Nothing at all. Just head over to the page and sign up. http://rewards.xbox.com/halo-4/