You can increase your stamina gradually by incorporating any aerobic activity into your regular schedule. Jogging, brisk walking, cycling and swimming are some of the aerobic activities that you can do. You can take up any of these activities but make sure you gradually increase both the duration that you are doing them for and the intensity with which they are done. To give you a starting point, try to do at least 10-20 minutes of any (3-5 times a week) and then slowly build it up to about 30-40 minutes. At a later stage, (about 3 months of regular training) you can also include what is known as interval training. That is short bursts of high intensity work, interspersed with medium intensity activity during each of these attempts.