Best way to improve stamina

If you're talking about physical stamina, the best way is to start running on a treadmill. On your first go, run as much as you can in one stretch to see where you stand, and then set goals and slowly work your way towards them. For example, if on your first go, you run half a mile at a stretch, then make it your goal to run 3 quarters of a mile and then a mile continuously without stopping. Also, while running keep track of your heart rate. The maximum recommended heart rate is about 220 - your age. For instance, in my case, it's 220 - 20 which is 200 beats per minute.

Along with just running, you should try and develop a proper gym routine and follow it religiously. Nothing, and I repeat nothing, is a better way to boost your energy than to hit the gym. It will take a few weeks, but you will be able to feel the differences in your energy levels. It is so worth the effort.