What's Your Advice for a First-time Marathoner?

Recently I was in a hotel gym and struck up a conversation with a triathlete. I mentioned to him that I was training to run the NYC Marathon for the first time and he gave me a piece of advice: don't go out too fast!

 "Make sure you don't get swept up in the excitement of your first marathon and go out too fast. It is easy to run the first 6 miles at a much faster pace than normal due to the adrenaline rush provided by the cheering crowd. This is a classic rookie mistake. It will cause you to burn through your energy store too fast leaving you with less energy for the 20 miles ahead."

This made perfect sense and reminded me of the old adage: "It's not how you start the race that counts, but how you finish."

It seemed so obvious once he said it, but I hadn't thought of it before then. Which makes me wonder what else I haven't thought of.

So, what advice can you offer this first-time marathoner?