If it is discussed in lecture it is important. The more time spent on it the more important it is. Note and study all figures presented in lecture and lab. Each individual must find the best method for them. This may even vary for a given individual depending on the subject matter.
Repetition is a key component necessary to move information into memory.
As an absolute minimum you should plan to review the material three times, in lecture, in reviewing the lecture, and in reading the text. This should be active review during which you organize your thoughts and test yourself. Actively studying requires effort, learning is hard work. It also takes time, there are no shortcuts. The following is a compilation of many of the techniques used by successful students to study.