I don't know about most, but I can tell you how I did it, maybe it will help. After my first marathon, the goal in my second marathon was to run a PR. I averaged somewhere between 6:15 and 6:20 pace the first time, so the second time I tried to run 6:00 pace for as long as I could and see if I could hold on until the end. It turned out I ran almost the exact same time, although the course was significantly slower. For my next marathon, I had run a half about a month earlier at 5:40 pace, so I figured I was in better shape than before and decided to try to average 6:00 pace. My goal was to go out and run 5:50 pace for as long as I could (even at the end of the half marathon, a 5:50 mile felt relatively slow), and assumed I would slow down towards the end because I figured I'd probably feel like crap no matter what and I can probably run 6:10 miles forever, and this is basically what happened.
But honestly, I think you should RUN HOW YOU FEEL. The biggest mistake I made in my marathons was slowing because I was afraid to go too fast -- for my first marathon, I hit 10 miles in 60 minutes and by 13 miles I had started panicking that I might not be able to finish (it was faster than I had expected), so I slowed down a bit from 13-19, and picked it back up again after that. I probably could have easily run 60 seconds faster if I hadn't slowed down there. In my last marathon, my first mile was 5:40 and I didn't feel like I was exerting myself at ALL, but I knew I was aiming to run 5:50's so for the second mile I slowed down intentionally to try to run 5:50, but ran 6:00 instead. Then I had to pick it up again to try to run 5:50 (which I did). I think that changing gears like that took more out of me than if I had just listened to my body and ran how I felt -- the result would probably have been 5:40, 5:45, 5:50 instead of 5:40, 6:00, 5:50, and I would have probably felt better about it too.