Learn to tell people to back off about three years earlier than I did. Being able to say "No, I am not okay with that and don't tell me that I am." is something I wish I had learned a lot earlier. However, this is usually learned best after 18 when you actually have the paperwork to enforce it. And by extension "S/he with the most documentation wins and gets to do what s/he wants.". I wish I had learned that before my freshman year of college.