The best way is to find an animation school and do everything you can to get enrolled.
While you're still in high school, I would suggest drawing every chance you can.
Also, get some books on animation. I'd especially recommend Cartoon Animation by Preston Blair and Character Animation Crash Course! by Eric Goldberg. Both can be found at amazon.com
Don't fall into the trap of thinking that because you might want to work in CG animation, that you don't need to know how to draw. It's extremely important to learn how to make something look good on paper, before you can make it look good in a computer.
Also, I'd suggest getting a copy of anime studio, adobe flash or some other animation program. You can really learn a lot just by experimenting yourself.
Hope that helps