This guide to growing your hair long is primarily for males, but I suppose it would not be very different for females.
Growing long hair is very time consuming, obviously. It is a difficult transition for many people, because the process is a lot like getting braces. You'll look and feel strange for awhile, but suddenly you'll be beautiful. A change in hairstyle can instill a great deal of confidence in a person, and give you a whole new outlook on life.
First, make sure you can do this. It's really not so hard, when you think about it financially. Simply don't get a haircut. Get a friend to cut your split ends every once in awhile, but not too often if you want to grow your hair as quickly as possible.
Live your life, wash your hair every day thoroughly, and comb often; good circulation to your scalp helps a lot. After a few months, your hair will be really annoying. It'll be tickling your ears, jabbing you in the eyes, frustrating you constantly. And there's not a whole lot you can do about it either, since it's still too short to tuck behind your ears. Some suggest wearing a hat, but I myself used gel or mousse to style it so it stayed put.
After styling it for several months, I suddenly realized that my hair was long enough that it went past my ears. I started wearing it without the mousse or gel, and it felt just fine. Once you've reached this phase, you've past the largest obstacle. Now just let it grow, grow, grow.
I started off with very short hair, your basic nondescript hair cut that is reminiscent of Bill Gates. My hair was shoulder length by the 9th or 10th month, and I tend to keep it at that length. From there, you can grow it as long as you want, but if volume and body is what you want, keep it relatively close to the shoulders. Any longer, and your hair gets too heavy, and just becomes straight.
Good luck, and happy hair-raising!