Read ahead to the chapter or class slides that will be covered in class. This will ensure that you don't go into class unprepared, and possibly with some questions prepared. Re-read your notes/lecture slides after every class, preferably not long after learning the material. As you review add more notes to what you have already written and fill up any gaps using the help of the internet, tutor, or instructor.
It is better to be consistent and study a little daily, rather than leave everything to the last minute. Reading ahead for 30 minutes before class and 30 minutes after it, although it doesn't seem much, the discipline of doing it constantly will allow you to retain the information for longer. Leaving long periods without studying will make your retention of the material decline as time progresses. Look up Ebbinghaus’ forgetting curve to learn more about the phenomenon. Before any assessment, you could review for longer periods, making sure that you take healthy breaks in between to avoid burnout.
Chemistry involves a lot of math. For any problem that might be longer than one simple calculation try to implement a roadmap of steps to get from A to D. Think of this method as if you were writing a recipe. Reflect, why are you doing this calculation? What would happen if you changed a step? How would the result be affected if you interchange quantities? Etc.
Start the assigned problems/homework the same day they are assigned, when the information is fresh. Try to work out the problems on your own before using any kind of help. If you’re unable to solve the problem within 30 minutes, please don’t hesitate to seek help! It is a waste of your time to spend hours on a problem; you can build up frustration as a result.
Explaining the content you learned to a classmate/friend will help you grasp the material and possibly help them with any gaps. Both can also help each other with their respective questions.