Prior to attending FIDM for Graphic Design, I had no formal training in design, art, or any other related fields — I never even took an art, photography, or yearbook class in high school. However, one of the best aspects of FIDM is that incoming students are never required to have any formal previous knowledge of their major! Hence, it will not be imperative for you to have expertise of design and color principles, nor the programs. Regardless of this, I still used my free time to check out design blogs and magazines, look up tutorials, and practiced designing by emulating what I saw.
Taking classes in high school to familiarize yourself with your major is undoubtedly a definite leg up on others, but the first year of FIDM is dedicated to teaching students the basics; by the time your second year comes, everyone will mostly be on the same ground when it comes to principle and technology fluency.
My advice to an incoming FIDM students would be to keep yourself updated on the news in your industry. Be it Fashion or Graphic Design, know who the pioneers and game-changers in your field are. Knowing the masters of your field and their work will give you a clearer sense of direction and, ultimately, bring you closer to your goals.
Hope this helps!