Tips to increase penis size:
You should do the following from the ages of 14 to 21.
1.Stay lean, thin and muscular with exercise such as running and weights.
3.Don't masturbate too much, and when you do, don't damage penis by applying too much pressure
Exercise increases testosterone, the male hormone. Weights are especially good for this.
Being thin means less cholesterol (the fatty stuff that clogs blood vessels), consequently testosterone is more effective.
Being thin also means there is more blood flow to the penis; so when you get spontaneous erections it stretches out the 3 spongy chambers of the penis. See diagram: http://en.academic.ru/dic.nsf/enwiki/265769o
Don't masturbate too much as this depletes energy and effects hormone levels. The penis was not designed for the strong pressure of the hand. Over-masturbation is likely to damage the delicate spongy chambers of the penis. This leads to energy being diverted into repairing the penis rather than growth.
I would avoid spending time on the computer as this resists the temptation to look at porn and masturbate. Also the electro-magnetic radiation from the monitor is not good for you if your head/brain is too close to it.
You should be getting spontaneous erections. Erections are good for expanding out the penis with blood. This happens a lot during sleep.
So be thin, muscular and don't masturbate too much.
Other masculine traits will result from this too: deep voice, wide angular jaw and pronounced chin, pronounced forehead and big space between eyes.
Here is a porn tumblr that displays very large penises. note that nearly all are skinny and muscular: http://angloselfies.tumblr.com/archive