Avoid these mistakes to help ensure success in your chemistry class.
1. Don't Show Up
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.
2. Don't Practice Problems
Some of chemistry is understanding how things work. Some of it is outright memorization. Most of chemistry is learning how to set up and balance equations and work various types of problems. The best way to master these skills is to practice. The worst thing you can do is just copy another student's work or the answers from the back of the book. Do your work. Show your work. Practice different types of problems (often).
3. Don't Read the Text
... or the handouts or the lab manual. Reading conveys concepts. If you don't read, you don't need to worry about learning that pesky information. That said, it probably is more important to give special weight to whatever the instructor emphasizes in lecture. Don't ignore reading assignments, however. For chemistry, it's better to read the text before the lecture. If the lecture makes no sense, you need more preparation before class, which involves time with your textbook.