For improved orgasms and better staying power, there are a series of exercises you could commit to. The first thing you need to determine is where you are going to do your 'penis workout'. You can do these exercises nearly anywhere, but the best places are on the edge of a chair, with your buttocks against a table, or on your back, legs spread and one leg up. It may be worth doing them also in front a mirror to determine that you are doing them correctly. On a side note, all of these exercises should be done when the penis is flaccid, and be sure to pull the foreskin back before starting if you have not been circumcised.
Grab the head gently, and stretch your penis in an upwards direction. Keep it stretched in the position for ten seconds. Repeat this procedure but hold it in the downwards, right side and left sides respectively. Repeat the four-way pull for five minutes, and then do the entire thing at least twice a day.
Hold the head and pull the penis away from the body. Place your thumb of the other hand on the shaft, at the base of the penis. As you begin to lift the penis up with your hand, press down with your thumb, to create a curved effect. Once held in this position, keep it for ten seconds. Repeat this technique for the right and the left, but placing your thumb on alternate sides of the penis to create the curved effect again. Keep repeating this three-way motion, never going downwards, for five minutes, and do this exercise once or twice a day.
Place both thumbs on top of your penis shaft, with their nails touching, and then your remaining fingers underneath the penis to support it. Firmly then press the skin back into your body, but be sure not to press too tightly to stop circulation. Hold it firmly in position for ten seconds and then repeat after a short relaxation period. Essentially, you want to continue a pumping action, and the further back you hold the skin, the better results you will see. Repeat this once or twice a day for five minutes. Note that you can perform this when semi-erect.
Place one hand at the base of the penis and the other behind the head. Stretch the penis in both directions, with the one at the base towards your body, and the one at the end away from the body. Hold this position for ten seconds and then keep repeating for five minutes. Do this exercise just once a day.
Over time, you should hopefully see some change, but it is always best to seek medical advice. Be sure that you never to go to extremes and potentially harm yourself, all in the name of a larger penis.