Don't Blow Up on the Bike
Perhaps the easiest place to lose an Ironman race is on the bike. You've most likely just spent over an hour moving like a senior snail in the water, so the temptation on the bike is to hammer the pace. Luckily, technology can come to your rescue. If you have a power meter, use it during the race and know your upper limit of wattage. The best way to blow up your legs is to use too much power going down hills. It would seem (especially to many newbie triathletes) that you use more power and strength to climb up hills, but you can easily use more watts in pushing your big gear flying down the backside of hills.
If you don't have a power meter (they're very expensive after all), a heart rate monitor is the next best tool in your arsenal of race technology. By the time you're racing an Ironman, you should know your personal heart rate zones and, during an IM race, you should rarely exceed zone three to maintain your legs and stamina for the run.
It's All About Conserving Energy
If you've stuck to your swim and bike Ironman race strategy, you should have enough energy left in the tank for the marathon.
The good news: Unlike shorter races, you have enough time and real estate in an Ironman race to come back from a bonk. The bad news: You won't enjoy the bonk and you won't be fast.
The best way to avoid bonking on the run is, once again, to have a plan and stick with it. If you've done everything correctly you should be hydrated and fueled up enough from the bike portion of the IM to have the energy to run and maintain your target race pace.
What's your ideal race pace? The fastest you can go without bonking or walking. Again technology comes to the rescue. If you have a GPS watch, use it on the marathon to get your exact run pace. If you've trained at 10 minutes per mile pace, that should be your race pace. Keep in mind that an Ironman marathon is generally about 5 to 10 percent slower than a standalone marathon. That means that if you've run a standalone marathon before, adjust your pace and expectations, and plan accordingly.
If you don't have a GPS watch, do the math and figure out your pace the old-fashioned way. And remember to watch your heart rate. You should be in heart-rate zone three or occasionally four if you plan to run, not walk, across the finish line.
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