We aren't talking about taking advantage of those free point giveaways that pop up now and then. You know, the kind that just asks you to register and then they e-mail you a code for 100 MSP or something and some people use multiple e-mails to score a ton of free points. Yeah, that is kind of shady and not what we're after.
What we are talking about is using Xbox Live Rewards and Bing Rewards - two official programs from Microsoft that offer you free points for very little effort on your part.
Xbox Live Rewards
All you have to do is register your Gamertag with Xbox Live Rewards (you'll log in with the same name and password you use for Xbox.com / Xbox Live) and then you'll earn points for renewing Xbox Live Gold subscriptions and other things. New users will also be rewarded when you make your first Xbox Live Marketplace purchase or start using Netflix. You also will earn points for filling out a quick survey on the Rewards website each month. When you build up 100 MSP worth of rewards, those points will be added to your account by the 15th or so of the following month.
Now, it has to be said that you won't earn a ton of points super fast with Xbox Live Rewards, but they do add up. Once you are registered, things happen pretty much automatically so you don't even have to think about it. I've earned 880 MSP in the last year doing basically nothing out of the ordinary. It doesn't sound like much, but getting essentially a free XBLA game or piece of DLC for free is certainly better than getting nothing at all.
Bing Rewards is a program where you earn rewards by using Bing search. You have to register at the Bing Rewards homepage and, once you're a member, you'll earn Bing Credits for doing searches using Bing or clicking on specially marked Rewards links. Generally you'll earn only about 13 credits per day, but there are extra bonuses now and then that let you earn more. A 100 point Microsoft Point code costs 125 Bing Credits. So, in roughly 10 days you'll earn 100 MSP.
Again, like Xbox Live Rewards, it doesn't sound like a lot, but you don't have to put any effort into it. You just search like you normally would and earn free stuff. There is no downside here. In the year or so I've been doing Bing Rewards, I've earned about 2000 Microsoft Points. 2000 extra MSP for not really doing anything differently than I would anyway. It does require you to use Bing instead of Google, but it isn't a tough switch considering how "evil super villain-y" Google has seemed lately.
You can also use your Bing Rewards Credits on other things like Xbox Live subscriptions, gift cards for Amazon and other retailers, and more.
Enter Xbox 360 Dashboard Contests
Another way to earn free stuff is to actually enter the contests and promotions that pop up on the Xbox 360 dashboard all the time. You know what I'm talking about - the promotions for cars or Doritos chips or Wendy's or Taco Bell and whatever else where you just have to download a free gamerpic to enter. Do these! You can actually win and, again, there is no downside. You spend a second downloading a 108kb gamerpic and are entered into a contest. Since these are contests and up to chance you aren't guaranteed to win anything, but for no effort you definitely can win something, and that is better than nothing.
Over the last 5 years I've won twice - a 12 Month Xbox Live subscription from a Grand Theft Auto IV promo, and more recently 400 MSP in a Wendy's promo I honestly didn't even remember entering. Free stuff for doing nothing is awesome.