Muser,
I'd spend a bit of time going through the FAA site so you get the facts. The UK and Australia have "how to" sections on their sites so I can only imagine that the FAA does to.
Spend some time researching what the majors want academically so you get that bit right while you're young. They will also have hours and experience listed there too. (I hope) Look for "careers" in small print on their websites.
As a rough guide, they prefer ex military pilots or pilots with a degree (any I believe but "science orientated" are preferred) and a lot of hours in commuter + size aircraft.
American Eagle commuter airline.
If airline flying doesn't appeal, there's corporate flying and a whole host of other sorts of flying out there.
Corporate aviation is not quite so fussy about a degree but they still need hours. An example,
NetJets USA Pay attention to the "other attributes".
Right now. OK.
Do the best you can at school. Pick subjects that you're good at and get the highest grades.
Do you play team sports? Do something to show team spirit, cooperation, leadership and so on.
Do you have any preconditions that would stop you from flying? Bad eyes, bad asthma, diabetes etc?
Find your nearest airfield and go say hello to some folks. If you can go gliding, do that. It's a good alternative for you at the moment plus you'll meet people who aren't necessarily trying to get you to sign up to some expensive training programme.
Get a part time job if money's an issue. You'll need every cent you can get your hands on if you don't get into military flying.