AIf you haven't already, research. If you know people who are currently in university or have recently graduated, talk to them. Ask for tips and ask what their course was like. You can go to a library and go through books like college board's 'book of majors', or go through law or business books. If you get to know the material it'll help you find something you enjoy and maybe eliminate a few options. Another thing you can do is start by checking out universities, see which universities are of your standard and which ones you like, then go through their list of courses, check out the course details and modules, and pick your favorite course. Look at as many course listings as you can because you'll find more unique courses that way (some courses aren't offered in every university). A lot of universities have videos explaining the key points about certain courses as well and these can be really helpful (even if you think you aren't interested in that particular course, watch them. They'll help you be certain and sometimes you'll find out it's nothing like what you expected.) A good thing to do is start with a clean slate and an open mind: consider everything. Don't eliminate any courses without doing a bit of research first. This way, you'll be introduced to some new ideas and hopefully you'll come across something you like.
Once you're done researching, make a list of the courses you liked, then find out what the job prospects are for each one. Find out what career paths you can take and what the salary is like. Then you'll be able to eliminate anything that isn't 'highly employable'. If you're lucky enough, you'll form a career goal, then you'll be able to say "I want to get to point Z. I can take the following routes:.." (consider things like whether or not you need/want a postgraudate degree to get that job, and if yes, which undergraduate degrees would allow you to get there. Usually you don't need to study the same subject for both your masters and bachelors, but it helps to have a degree in a related field.)
Try to find out as much as you can about what both studying and working in your chosen field would be like. Usually, liking the subject you're studying makes it a lot easier to succeed in it. Don't forget that work experience is usually more valued than learning experience, so try to consider more than just employment rates: think of what you want your next four years to be like as well as where you'd like them to lead you.