What is the best way to build stamina?
Exercise by doing sprints, whether swimming, biking, or running. Take shorts recoveries making sure you stretch. You could also run for a long period of time or distance. You could also do cardio workouts. You can easily find some on TV.
Running and doing cardio workouts as much as possible...
Exercise regularly and eat lots of fruits and vegetables (especially broccoli, it has a LOT of nutritional value) get some grains and a lot of protein.