What are the first steps to create a subtle preppy style for a teen male?

I want to wear those cardigans with a shirt, and the light jackets. No ties though. I'm not looking to go all out. No scarves either. Pretty much, I want to have an actor's look. I am an actor in my school, and I want to dress the part. If you (the answerererer) could give me some tips on how to start, where to shop, and how to "execute" the style properly.