Recovering from your training
  Many runners fail to realize that one of the most important aspects of marathon
  training is the taper phase. Reducing weekly and long-run mileage during these
  final two weeks is vitally important so that you will be fully recovered from
  previous workouts while at the same time be completely rested for the big event.
  Assuming that the marathon is scheduled on a Sunday, we will refer to the taper
  phase as the time that spans the two weeks prior to the marathon right up to
  Saturday night before the race.
Final preparations for the big race
  Cut back on the distance and intensity of your training runs during the two-week
  period prior to the marathon, eliminating long and hard efforts. You will need
  to make a decision whether you wish to take either (or both) Friday or Saturday
  as a complete leg rest day on marathon weekend. Remember, there are no workouts
  the week prior to the marathon that will enhance your preparedness for the race.
  An important rule of thumb is "less is best," particularly if you
  are feeling either physically or mentally tired or your leg muscles are fatigued.
  Keep stretching as much as possible during the couple of weeks prior to the
  marathon. Consider getting a leg massage no more than two days before the marathon,
  but if you've never had a leg massage, don't try it now!
Getting off to a good start 
  On race day itself, line up according to your expected pace, remembering that
  the fastest runners will be at the front. While runners are generally very honest
  people, this often does not hold true when they are asked to position themselves
  for the start of the race! Unfortunately, too many slower runners line up in
  front of the faster runners. In addition to this not being fair, in a large
  race, the slower runners can actually create a dangerous situation, as people
  tend to be pushed down or slip and fall. Don't get too caught up in the initial
  excitement by being overly exuberant and yelling and cheering as the gun is
  about to go off. Save that energy for later, when you'll need it. Instead, focus
  on positive thinking. Visualize all of your friends who will be pulling for
  you and all the hard training that went into the preparation for this big race.
 Start well, end well
  Running the correct pace for your ability level is crucial in the marathon,
  especially for the first-time marathoner. It's so easy to start the race by
  running at a pace which is much faster than you are prepared for. Your pace
  during the first mile often feels effortless due to the adrenaline rush and
  excitement of the event. If you run the first mile or two fast, you'll pay dearly
  for the mistake in the later miles. A much better plan is to start out slower
  than what you hope to average and then run the middle miles at your chosen pace.
  Then you can pick up the pace during the final miles when you know you can finish.
  In the world of marathoning, there's no such theory as "putting the fast
  miles in the bank early in the race" and then holding on in the end. If
  you go that route, you will most assuredly visit the dreaded "wall"
  - the point in time when glycogen stores within the muscles have been depleted
  and, as a result, the runner's pace slows considerably, often to a walk. 
Look after yourself during the race
  Do not pass up any fluid stations on the marathon racecourse. While it's acceptable
  to drink just water in the early miles, runners must consume sports beverages
  no later than 90 minutes into the race (and earlier if possible). Find out what
  works best for you in long practice runs. At a fluid station, water is usually
  offered at the first tables with sports beverages served near the end of the
  station. If you're not sure what's in the cup (water or sports drink), politely
  ask. Squeeze the top of the cup into a "v" shape to create a smooth
  delivery of fluid directly into your mouth if you choose to run and drink as
  you pass through. If necessary, walk through the aid stations to be sure that
  you are able to consume the entire contents of the cup. If you choose to stop
  and drink, be sure to stay out of the path of approaching runners.
 Running with others
  Often during the marathon, you will encounter other runners who will be running
  your pace and may wish to engage you in conversation. It's a personal decision
  as to if you wish to stick with them and chat along the way. The positive aspect
  of socializing is that many great friendships have been started this way, and
  that talking to others is a great way to take your mind off the physical discomfort
  you may face later in the marathon. On occasion, runners who are experiencing
  great difficulty in the later stages of the event make pacts with one another
  for a motivational strategy as a means of finishing the race. However, talking
  may rob you of valuable energy you may need later. The last miles of the marathon
  can be quite draining mentally. For that reason itself, you may choose to run
  the last miles without much conversation. Also, running with someone may slow
  you down. You'll undoubtedly finish the marathon, but sticking with someone
  slower may compromise your chances of achieving a personal goal.
Adapted from "Marathon Training Program: Final Race Countdown and Marathon Strategy", by Art Liberman.