As you approach your junior year in college, most schools will offer you internship opportunities, organized through the department in which you major or through career services. Take the opportunity to find and use the internship experience. It will give you a better feel for what life after college will be like and will earn you experience and sometimes even college credit in your major.
Even unpaid internships or those with housing stipends only may be right for you if they give you a leg up on the competition when it is time to get a job. It is important to note that many times an intern will be offered a full time position when they graduate, so if you like the company in which you work and the people you are working with, you may not even have to look for a job after college. In this competitive job environment, that is a real advantage!
The closer you can get to the department or job you think you want, the better you can assess the position in advance. Though you may feel that you are committed to a certain position or type of job by your major, if it is not right for you, it is better to know that before you graduate. You may still have time to add some courses and create a double major that will take you in another direction or to come up with a plan for beginning work in a particular field and going back to get a different degree in graduate school.
If the environment in which you are working allows from some flexibility in applying your major and area of study, you may also be able to explore other jobs in the same field and find one that you like better before you graduate. Use your time as an intern to meet with and talk to people in the company who can help you make a decision and give you more detailed information about the job you think you want. Most people are happy to talk to you if you ask for help, and you may just find a mentor and champion you can use after graduation.
If you graduate without having dipped your toe into the work pool, you may have a rude awakening when you get a job and discover that the company, job or tasks are nothing like what you imagined. Assess your options for internships early so you can apply for and find the best ones before everyone else grabs the good jobs. Talk to your professors and to career services and keep an open mind about suggestions they make. You may be surprised to find that you like what they suggest and that you are quite happy in the position they recommend. Remember that internships give you a chance to test the waters. Take that opportunity and use it to your advantage in getting a good job (a job you like) after you graduate!