It is best to check course pre-reqs, co-reqs, and restrictions before registration opens. This will allow you time to get appropriate signatures or make other plans for your schedule. You can check the course pre-reqs, co-reqs, and restrictions in the course descriptions listing by clicking the CRN (Course Registration Number) in the Schedule of Classes or by looking at the undergraduate course descriptions.
When registering, if you get an error, read the error. Many times the error is due to a time conflict or lack of a co-requisite course (i.e. MA2160 has a required Recitation and Lab). You can easily correct these errors by selecting a class at another time or adding the co-requisite course. If you still are unable to register, check the course pre-reqs, co-reqs, and restrictions to see if you may need a waiver.