For alot of corporate jobs, your career starts before you actually enter the workforce. It starts right on campus! How so? See below
Coursework
Your future employer is of course more likely to see you more favourably if you study something related to their area of business (especially in more technical fields like Law or Engineering). However, if you change your mind, don't despair! You can always change your area of study by going to grad school, and you may not even have to if you want to enter a more "generalist" industry (like management consulting, corporate business analyst roles). I've known Partners at consulting firms who studied Linguistics or Literature, and big-time CEOs who didn't go to college / university at all!
In selecting your area of study - my suggestion would be to follow your passions. Even if it doesn't pan out, you'll never end up second guessing "what could have been"
Extra-curriculars
In addition to being a TON of fun and a great way to meet like-minded friends, this is a really great opportunity to show that you have leadership and teamwork skills to your future employer.
When you first start at college / university, scope out what clubs and societies you're interested in, and get involved from the beginning! It's a great way to make friends and connections, and the more involved you are, the more trust the team will have in you, and the more likely that they'll want to have you on to lead the group as time goes on
I know some people who only join "vocational" clubs (for example, a Law students society, or a Business school society). I think this is fine and makes your passions clear to your future employer, but you probably want to also show a side of yourself that sets you apart from the rest. If you're part of a sporting club for example, that's going to be a great conversation starter later down the line
Networking
Most colleges and universities will hold great career fairs, career talks and networking events to get their students out there. This is a GREAT opportunity to help you understand what careers are open to you and what you might be most interested in, as well as to meet people who are in those careers who may be able to give you good advice on how to get in.
Dont be shy! Ask lots of questions and establish rapport where you can. If you establish a good enough relationship, they may even put in a good word in for you during a future application process, which will boost your chances of getting in significantly