There are probably a lot of students in late high school and early college that are wondering how to become a financial analyst. As a person who has worked in this industry for a long time I would tell them to begin preparing themselves.
Realistically, they will need to go onto to grad school and get some significant experience under there belts before they take on any real responsibility in a corporate setting. But while they are still young and in school the can do a lot to improve their career later in life.
Find an industry that you are interested in and begin studying it intensely. Look up information online and follow the trade journals. Become an expert as quickly as you can.
Learn the ins and out of the financial markets and begin to study the way their influence ripples through the economy.
Finally, talk to as many business people as you can. You can learn a lot from their experience. Sometimes the best way to be an analyst is to look at what people have done before.