@torridall, I would suggest taking on an internship related to thing you want to major in–I did so and it provided me with new insights in my concentration, let alone a nice line in the resume. Also travel, I believe that would make a transition to real life easier. Having traveled and communicating with various people from different backgrounds, I broke the academic bubble I gained new perspectives on what I intend to pursue as well as learnt to accept the diversity of the world. Take up some hobby bc you’ll be very bored after the application process is over.
@Ciella, I took SATs in some international school I have nothing to do with. I prepared for SAT Subject Tests on my own. For SAT Reasoning Test, the only tutor I had was an essay reader.