Possibly one of the easiest ways to ensure failure is to not attend class. It's possible to teach yourself chemistry without ever setting foot in a classroom, but learning a subject isn't the same as passing a class. If you don't put in the time, you probably won't know what is expected of you for exams. You won't know what problem sets are due. You can't do labs if you aren't there. Even if there isn't an attendance policy, it helps to put in face-time.