In high school, you probably took between six and eight classes each semester and had many of those classes at least three or four times a week. College doesn't work that way. In college, some classes may meet only once a week, but the material that you need to study for each class takes up as much time as your high school classes used to, if not more. That means that these classes are designed with the idea that you'll only take a few classes each semester.
Looking at how many credits a class is worth will give you an idea of how much of your time it will require. For example, if you have to take twelve credits to maintain full-time status at your school, you can arrange your schedule so that you're taking three four-credit classes (three difficult classes with lots of studying and coursework involved) or a handful of two-credit classes (such as yoga). Even if your school allows you to take a large number of credits, it isn't recommended during your first semester. Most people mix it up each semester, taking a combination of difficult and easy classes to avoid burnout.
With all of the variety available, there will probably be quite a few classes that call your name when you first take a look at the course list. However, you should consider the courses you know that you'll need to take for graduation and try to get some of the basics out of the way during your first semester, especially if they relate to classes you took in high school. That calculus course will be a lot easier if you take it while everything in high school is still fresh in your mind.
It's possible that you've come to college knowing exactly what you want to do with the rest of your life. Even if you do end up entering that profession (which would put you in a minority, as most students change their majors at least twice), you don't necessarily want to fill up your schedule with classes in that major. Treat your first semester as an introduction to the college experience as a whole, and take a variety of classes so that you can be exposed to different things. For example, you could take one course that relates to the major you're interested in so that you can learn more about the field, but taking other courses that fulfill your general studies requirements will introduce you to a wider variety of students and knowledge.
In college, much of your studying and coursework are done on your own time, with relatively little time spent in the classroom. Take advantage of this fact by strategically planning your schedule according to the times and days the class is offered, as well as what you want to take. Arranging your schedule so that all of your classes are on Tuesdays and Thursdays gives you three weekdays to get a job or focus on other interests. Taking all of your classes on Monday, Tuesday and Wednesday means you have a four-day weekend if you're interested in going home to visit family. Also, if you know that you aren't a morning person, it's probably a bad idea to schedule a class that starts at 7 a.m., especially if it's the only class you have that early.