According to a study published in the International Journal of Sports Physiology and Performance, there's an easy way to shave as much as one minute off your 800 meter race time. Swap your regular warm up for a high-intensity run at a distance equal to approximately 25% of the race's length.
Researchers had 11 competitive runners race a pair of 800 meter time trails separated by at least a day. One the first try, they warmed up in a typical way with 10 minutes of self-paced jogging and six 50-meter strides. The next day, they ran a 200 meter distance at race pace after a 10-minute jog and a pair of 50-meter strides. That last warm up helped them achieve an average time of 124.5 minutes compared to 125.7 minutes.