Pace yourself. Get into a rhythm within the first minute or two, and when you start thinking, “I can maintain this,” back off from that about 20 to 30 percent.
Halfway is about 10 miles, in terms of how you should dole out your effort. Think of the final three miles as the second half.
Strike up a conversation and talk back and forth. What that does is create “conversational pace”: If you can carry on a conversation while you’re running along, you’re not going too hard.
You can only be anaerobic for about three minutes, no matter how fit you are.
Run for effort rather than time. Especially if you are running your first one, the goal is to finish it. Don’t have any time expectations at all.
Stuff You Should Have Done Two Weeks Ago:
Vary the warmup a little bit, so you know something different is happening. Bu still warm up as if you’re going to do one of your hard training sessions.
Scale down the workouts, so that you invariably do them well. You want to be reinforced, not discouraged.
Sometimes people rest too much. Don’t back off so much that you get antsy and feel like you’re not in your normal routine.
Nothing you do training-wise within those last two weeks will probably help you on race day, anyway.