All the hair on our bodies is strictly a genetic thing over which we have no control. THere is nothing that you can do to increase the amount, some of us have alot, some very little. Depends some on age and current stage of puberty (if you're still a teenager) Hope that helps!
I noticed that since I've gone back to work (school's our for summer) my hair has been growing a lot faster. I get a good beard going after a week without shaving, as opposed to about two weeks when I was in school.
My job is very physical and I eat a lot more. I'm in much better shape now that a few months ago. I've pretty much turned vegetarian as well, not for any reason, just meat doesn't seem to appeal to me when I'm sweating and tired. Maybe that has something to do with it. My fingernails also grow amazingly fast.