My racing philosophy is a simple one. It doesn't require formulas or splits. All it requires is that you run by your body and effort on the given day.
The reason for this is because predicting how you're going to race in the marathon is a bit like predicting the weather. You can be on or off, and when it's your first marathon, you don't have a lot of history to go on in terms of predictions. That's because there are so many variables that can affect your performance, some of which you can't control. You can control your training, nutrition and sleep, for the most part, but not the weather or illness. (Don't let rain ruin your race day—check out the Cool Gear Tip That Keeps You Dry.)
For example, if you plan to race at a 10-minute pace based on a 10K race you ran or your training pace, that can backfire quickly if the weather is hot, you have a headwind, or you're just not feeling all that great on race day. It's a little like picking the winning lottery ticket, and going by pace is not the most effective way to train or race.
Distance running is all about energy management. Pacing yourself from within will ensure a strong finish no matter what the clock says.
Here's a pacing strategy for the first time half or full marathoner. Run by color and tune into your breathing rate and perceived effort (how you feel on race morning).
Run the first 7 or 14 miles for the half or full marathon respectively at an easy, conversational effort (the yellow—a.k.a. "happy"—zone). If you can't talk to your buddy about how cute the shirt you bought at the expo is, you're going too fast. Slow down.