Get familiar with your owners manual and diesel supplement (extra book that specifies info for the duramax option). It will show you all the tricks on how to reset oil life counter, fuel filter life, etc... If you have the steering wheel controls, it is pretty simple. Otherwise you have to perform a sequence of events, like pump the accelerator so many times in five seconds etc...
Understand the consequences of things you do to the truck and be prepared to fix/upgrade parts if you run it hard/abuse it... For example, if you put a big tune on it and beat on it at highway speeds, be ready to upgrade the tranny...
Get familiar with the basics like priming the fuel filter in the event you or someone you loan the truck to runs it out of fuel. I have read several stories from new owners that end up paying a tow bill because of a lack of familiarity with their new vehicle.
Most importantly, get familiar with the various sections on this site. That way, if you notice unusual noises or something that doesn't seem right you know where to go to diagnose it or find help. There are so many guys that have forgotten more about the duramax than I will probably ever know. I couldn't begin to estimate how much I have saved by researching problems on this site and doing my own work. I am sure you will have a similar experience.
Congratulations and best wishes!
Robb