If you have a degree in mind, your institution usually provides you with a list of courses that are mandatory in order to graduate. Those are the first classes you should worry about when registering (for example, as a history major, I had to take specific classes on the study of history, world history, and american history otherwise I wouldn't be able to graduate).
However, there are generally various options within those mandatory areas. For example, I had to have 2 sciences with 2 labs, so I took Marine Biology and Historical Geology. I could have taken any variety of science courses, but I chose those because they sounded interesting. You can also check websites like "RateMyProfessor", etc. for information on which professors are easiest and sign up for classes that way - which can be helpful if you're worried about your GPA or if you don't want to have to stress out over assignments. I have taken elective courses with friends, but I made sure those electives would fit into the required elective area for my degree before signing up.
But truthfully, you're paying for your time at college, so you can technically sign up for whatever classes interest you. It's just a matter of how quickly you want to get out of college and how much debt you'll have to pay back once its over.