Great question! In addition to Rebecca's answer, which covers many factors which should be considered, knowing yourself with the DISC assessment is important. There is a student and career report which has suggestions for possible fields that are compatible with your strengths and behavior/personality. Another way is to volunteer in the areas in which you are interested in pursuing as a possible career. Happy to discuss this more.
Below is my suggestion :
1. Think you about what you have interest on. E.g. if you have interest in Maths, would like to become an accountant, banker, financial analyst, engineer, maths teacher, etc.
2. Explore more on these careers and identity a few careers you have interest on
3. Speak to someone who are working in these careers. Seek guidance from your mentor, school career counselor, your parents, etc.
4. Shortlist 1-2 careers you would like to pursue
5. Find out the entry criteria of the relevant subjects in the college
Hope this helps! Good Luck!
With a career, there will always be flexibility to adapt and hone closer to your interests as you go. Consider whether you like a desk job or one where you are out and about, do you like to socialize with people, or prefer to work alone, do you want travel to be part of your career? Look at what are the prospects in the market (what kind of careers are starting to have demand now), look at the pay for the types of careers you are considering. This may or may not be important to you, but if it's important to you, good to know ahead.
If you don't know what career you want to go into, but you know you want to get a degree, choose a broad degree (Business or Computer Science) both allow you flexibility across industries in a myriad of roles. The key to a successful career is to find something you are passionate about and apply the skills that you've learned along the way, to make a difference!