Well, I’m no expert. But here is what I would suggest:

1. Read as much as you can! Read about things you are interested in! I would take a glance at ethnographic accounts, peer reviewed journals (nature and science). Most online publications require you to have a subscription to them, but I think you can read things via Google Scholar. I highly recommend the Human Evolution Coloring Book since it covers a broad range of topics, and it is quite easy to follow (it was also written by one of my professors, and I like coloring).

2. Watch documentaries :) Netflix has some good ones. You can also probably download some titles online.

3. Look up field school opportunities for high schoolers (I wish I had did this before I went to college). You can also probably take anthropology courses at a local community college (you’ll also be able to get transfer credit when you go to college, and probably be able to opt out of some general education or lower division anthropology classes).

4. Start looking at colleges with amazing Anthropology programs and visit them!

5. If you’re more interested in the physical and biological side of anthropology, get a giant human anatomy coloring book. Personally, I find that anatomy is one of the hardest things to learn. If I could travel back in time, I would have wanted a head start on memorizing all the features on bones.

6. Develop a good writing strategy! The cultural anthropological world is mainly reading and writing orientated. You’ll have to read numerous books and journals and be able to deduce multiple points from multiple authors. You can practice by writing article summaries, and having argumentative theses.

I hope that helped :)