People you interview become part of your network. Keep in touch and ask them to let you know when there are any openings in your field. Friends and family can also be a part of your network, and they might be willing to help you in your job search.
LinkedIn is another good tool to develop your network. Start an account while you are still in college and add students who will graduate before you. Also, almost all colleges have an alumni/ae network you can use to meet graduates in your field. Try visiting the alumni/ae office for advice on how to connect with them.
Most importantly, stay in touch with your contacts, not only during college but after you get your first job. On average, employees only stay about three years at a job, so you will want to keep those contacts for your next search. In addition, you should pay it forward by helping other young job seekers. Keep in touch with your alumni/ae group for those kinds of opportunities.