When I went to purchase my last game I had a bit of a conversation with the manager of the video game store and he told me some info I wasn't aware of. He said to have your XBox 360 laying flat rather than standing upright. Being in the upright position the machines have the propensity to scratch the hell out of the discs in a circular motion. He showed me some of the discs that it happened to, and it wrecks havoc on the machines as well. Another obvious point was not to move the machine while a disk is either in the drive, or if the machine is running. That I knew, but I thought the other info was good.
Also, try to put something underneath the XBox so that it can get some cool air circulation going underneath the machine. That I knew too, but I figured that I would pass on that information.