1. Start shadowing doctors. The more experience you have shadowing doctors/hospitals, the more understanding you will have of the field and what draws you to it. You can also ask the doctors questions about their education and what they wish they would have done differently.
2. Unless your parents/family are going to be paying for your education, go where it's cheap! (And even if they are paying, I'm sure they wouldn't complain if you chose a cheaper college). Prestigious colleges are overrated when you are the one who has to borrow the money/pay. Go where you can get a scholarship, even if it's not a well known undergrad college. It's okay. As long as it's an accredited college and it has the major you want, go there. You will thank yourself later on when you owe less money than everyone else.
3. Choose a good undergrad major that will be your backup plan in case you don't get accepted to med school on the first try. It's okay if it's not science based. You will need to take the pre-requisite classes that the med school requires, but you can combine those with any major you like (it just might take a bit longer). What major would interest you if medical school wasn't ever a thing? That's what you should pick! Follow your desire. If you are going to spend 4+ years working hard and studying, you need to get a degree that you enjoy, are proud of, and can make you some money. Nothing wrong with a biomedical sciences or biology degree. But if it's really not your thing, then major in something else.
4. Once you get to college, make sure to map out all four years (or longer if that's the plan you chose) for the classes you need. Realize that college advisors can be totally wrong and they can tell you that you need a certain class that you don't need. Many people have this experience. This is why looking through the course catalog and fully understanding what classes are required are so important. Some classes are only offered every other semester, depending on the college/class, so be savvy about it and always keep an eye on your schedule. Unfortunately, advisors don't know everything and you don't want to be spending extra semesters in college when you don't need to.
5. Realize that you are going to fail because we all do. It sucks, but it's going to be okay. The real failure is when you don't get back up again and keep going. Even people who are doctors still fail sometimes and do the wrong thing, but they pick themselves up and they keep on going. They don't give up. They learn from the mistake and they don't do it again. Even if you fail a class, not the end of the world. You can retake it. It may hurt your chances of admission, but the worst thing to do is quit, Just pick up and move on and keep going toward your goals. It may take you longer to get there, but you can definitely get there.
6. Get help as soon as you need it. No matter what kind of help it is, please seek help when you need it. It isn't weak to ask for help. Get tutors in your hard classes (often they are free at universities). Go to the writing center and get help on your essays. Go to your professor's office hours and introduce yourself. Go to your medical doctor if you are struggling with feelings of depression/anxiety, etc. The resources are out there, but you have to be the one to push yourself to get help when you need it. Everyone needs help sometimes, so always keep that in mind.
7. This one is really tough, but you have to believe in yourself. Because there are people out there who don't believe in you and don't care. You may have an advisor who tells you that you aren't good enough for medical school and that you should quit. You may have a terrible professor who doesn't think you can pass their class. But if you know who you are and what you want, then you keep going. Be yourself, believe in yourself, and believe in your ability to get up when things are hard, and to start over again if you need to. This is something that doesn't develop overnight, but always remember that you are your own best advocate and that believing in yourself is a powerful thing.