Here are three quick ideas to build up your running stamina. Don't get stamina confused with endurance. Endurance is being able to run a marathon or longer, but very slowly. Stamina is being able to hold on to a fast pace for between 1 to 5 miles. Stamina is very important for what we called in college "Middle Distance Runners" or people who raced the 1 mile, 2 mile, or the 5k.
1. Do some Tempo Runs! This really helps because a tempo run is a distance run at a quicker pace.
2. Try running some intervals. This is where you run at a faster pace for a shorter period of time, but then you repeat this over and over. Examples would be running one mile repeats or 400 repeats on a track.
3. Fartleks are distance runs where you run slow, but every few minutes you pick up the pace and run fast for a while. You slow down and then pick up the pace again and again. It's called "Speed Play".
I hope these three ideas help you build your running stamina.