Like the rest of the guys and gals said, intervals is the key. I personally hate the treadmill for various reasons.
#1. Nothing beats open air, even if you´re down-town!
#2. You force yourself to keep a stady pace and rhythm rather than "comply" with the treadmill´s speed.
#3. There can be more adversity that you don´t notice so you´re doing more and feeling less tired (wind is a perfect example).
#4. That´s where the race will be. UNless you´re positioning treadmills in a line-abreast formation and see who tops the machine of first
Apart from intervals what I´ll do after a good 5 mile run with some inclines is right at the finish line:
Sprint 60 meters at 60% speed
Sprint 80 meters at 80% speed
Sprint 100 meters at 100% speed
And do it again....
Nothing beats ending a run by just lying on the grass and not being able to get up!
SOme more important pointers for various stages of the run are:
A. Watch your form. Don´t throw your hands around or slouch. Chest out, shoulders back, and use your arms to give you speed.
B. Use big strides and really push the tarmac with your feet. Don´t just up the tempo, bur rather pull with your hands and push with your feet.
C. When sprinting try to stay as aerodynamic as possible. That means watching how your arms extend, how your shoulders move, your palms streched out etc.
D. Watch your breathing. Keep it disciplined, rythmic, and inhale from nose and mouth, while exhaling from the mouth. If you feel you need more air don´t deprive yourself but don´t "break your rules" either. Simply up the tempo but still keep it rhytmic. Don´t just reach a point where you say "Screw it" and you start gasping for air!!
Make sure you have a well rounded nutrition, that you´re getting enough calories and that you´re getting your yummy carbs! (Too many women on Atkins diets these days...Too much carbophobia out there
Good luck on the race!