How do you grow long hair. HELP! please :D?

I have heard many different things on the net, and I know that hair usually grows maybe 6 inches a year. What products work, and which ones don't? I am a teen, and I would like my hair longer, maybe a little above my belly on. Also, does Mane n' Tail work? All help would be appreciated, thanks!! Also, I'll mention that I have thin straight hair and that my hair doesn't grow fast at all, hhehe. Alrighty,thanks!!