Pop on to the Rewards website frequently to find out about current promotions, typically there's a monthly survey of 5 or more questions that nets you 20msp credited to your Gamertag's points balance, with various other offers available.
The last big promotion of note was April's Triple Play offer, where Microsoft rewarded rewards members with a 300ms point credit for doing various tasks such as watching Youtube videos, renting a Zune film, buying an XBLA game or similar content.
Whilst I scored the bonus 300 ms points as seen in the image, I'll admit to shamelessly leaving my Xbox 360 on the Facebook app for an hour and enduring one of the suspect British soaps to pass the time away from Xbox. From the promotion's launch til now, besides my Facebook shenanigans and going out of my way to do 20ms point monthly surveys, everything else earned was gaining by simply doing what I would have done even without the existence of the Rewards scheme.
Think of Xbox Live Rewards as a cashback scheme, it's just that, but in Microsoft points form. Simply sign up at http://rewards.xbox.com and then just carry on as normal, and you'll be racking up some points without even being aware!
Soruce: msxbox-world.com
