Tip 1: The day before
Make sure you get to sleep early. That way you will spend the whole night turning and twisting in bed trying to fall asleep but unable to. When you finally do get to sleep it will be two hours past the usual time you sleep at, and you will wake up in a sweaty distressed state, from a dream involving wooden spatulas and your high school teacher.
Tip 2: Have a good breakfast
Now that you have woken up in the shittiest mood ever, and that your stomach is in knots, you should try to force some food down your stomach.This is very important, I know they will be giving out bananas and raisins and shit at the marathon, but you won't have time to grab that shit while you're making the dash to the finish line against a Somalian man 1/4th your weight. This is when your breakfast comes in handy, a well aimed projectile vomit can win you anywhere between 5-10 seconds.
of course this could happen as well
Tip 3: Drink lots of water
Water is the source of life, and coke and tea, and pretty much everything. So it's very important to keep drinking during the entire day. It is not uncommon for real marathon runners to keep running from the finish line to the bathroom having held in all that liquid while they were marathoning. Of-course being Lebanese I encourage you to take piss breaks regularly if you need to. Use the nearby tree, a wall, or even better a fellow marathon runner's leg for extra points!
Tip 4: Lose with honour
We know you will probably come last. Right after the quadriplegic cripple, what did you expect? Just make sure to lose with respect and dignity. keep your head high and hope that they have a prize for last place. You've done us all proud, and there will always be next year.