There is research that shows that the beat of the music helps to keep the pace of your run. Pretty cool, huh? So when you need to pick up your pace, pick a faster, up-beat song and it will help you push it even harder. Here is a link to check out that suggests songs based on your mile running time. Therefore, if you are a slower runner it will suggest slower songs, and if you are a faster runner it will suggest faster songs. Find some songs that are fit for your pace, or even a slightly higher pace to help you improve your run. Motivation by music!