First, as you are just now about to enter high school, know that you are ahead of the game. Many students do not discover their interest in architecture until well into high school or after.
Start by planning to attend one of many high school summer programs during your high school summers; for a list visit the following — Summer Programs. These are great opportunities to help you learn more about the process and determine if becoming an architect is what you want to do.
Next, learn to draw by hand — do not worry about drafting or CAD which is taught by many high schools. Instead, take ART or creative courses – drawing, painting, ceramics, etc. If your high school does not offer ART, simply buy a sketchbook and draw 30 minutes per day of everyday objects. You are trying to connect your brain, eye, and hand.
Also, explore and see the built environment around you. It is great to see the architecture around you but start with your own house. Become a detective and learn the materials of a buildings — why did the architect do what he/she did.
Contact local architects to possibly shadow for a day or so to learn more about the career. Visit architecture schools to consider but also to see what happens in college.
A last idea is to obtain a copy of Becoming an Architect, 3rd Edition. These ideas should get you started, but feel free to comment with additional ideas.