Taking notes in class is just one step in the process of studying. In order to utilize them effectively, you need to interact with those notes after class, and not just the day before a test! Ideally, you want to take out time to review notes you took in class within 24 hours after you've taken them.

Here are some ways you can "interact" with your notes after class:

Re-read them to generally review information.
Write down any lingering questions you may have about the material that you can research later, ask during the next class, or talk to your professor about during office hours.
Write down a summary of the information you learned in class that day in your own words, based on your notes.
Create a practice "test" based on your notes. You could create practice problems, or create notecards to quiz yourself on concepts.
Rearrange the information into a mind map/concept map. By doing this, you can visually see connections between concepts you went over in class and categorize things accordingly.
- Here are suggestions of different formatting for rewriting notes as a study tool.
Compare your notes to the instructor-provided notes/presentation and fill in any gaps.
Use active recall before re-reading your notes - write down all the information you remember learning about during that class, then highlight the sections in your notes that you forgot about so you can study those more closely.