It depends a great deal on your class year. A first year student may have a harder time getting into some courses than a senior.

The courses that fill up quickly tend to be the weird courses or the courses that are new and unique. There is almost always just one session per semester of these courses. For example, I took a course called Medieval Islam last semester. The course had never been offered before, so a lot of students tried to get in and it was hard for myself, a Junior, to get into the course.

There are more seats available to introductory courses, but they can get filled up really quickly too. These courses are often required as an LSR for all students, so everyone will have to take them at some point. There are also multiple sections taught each semester for most of these. They can be difficult to get in, but there are so many options that you'll find something.

By the way, Course Registration happens in waves. It goes from Seniors, Juniors, Sophomores, and First Years. Each class is randomly divided into groups and assigned a day to register. They can only register on that day. There are also open days after the regular ones where people can register for classes.

That's about it from me. Catch you later!