Don't just re-read your notes. When you first read, you extract a lot of information, but when you do it the second time, you read with a sense of 'I know this, I know this.'
This gives you the illusion that you know the material very well, when in fact there are gaps.
Read once and then quiz yourself. Retrieving that information is what actually produces more robust learning and memory.
Even if you get the answers wrong, you'll still have an idea of what you don't know. This helps guide your studying more effectively.
Relate new information to prior information for better learning.
During a second reading, try to connect new information to something you already know.
Draw out the information in a visual form: diagrams, visual models or flowcharts.
Anything that creates active learning, that engages you and helps you generate understanding on your own, is very effective in retention.
The key to using them is re-testing yourself on the ones you got right.
Encountering the correct item again is useful. You might want to practice the incorrect items a little more, but repeated exposure to the ones you get right is important too.
Don't cram. Research shows this isn't good for long term memory. It may allow you to do okay on that test the next day, but you won't retain as much information in the long turn.
The better idea is to space repetition.
Mixing lessons and examples produces much better learning that can be transferred into the real world.
You're going to have to figure out the method you need to use for specific situations. And you can't learn how to do that unless you have experience dealing with a mix of different types of problems, and diagnosing which requires which type of approach.
This related to the 2 types of mindsets: fixed and growth.