There are many ways to approach note-taking (the outline method, the charting method, the mapping method, the sentence method, etc.), and it is important to find a style that works for you. The style you choose may even depend upon the class that you are taking. One of the most popular approaches is the informal outline method (which I used as an undergraduate and graduate student). Another popular approach is the Cornell Method (aka Cornell Notes), which usually combines the informal outline with an extra couple of features that will help you organize and make sense of your notes after class.
Click on the pages underneath this one to read about these methods.