Although I'm a few years (well, alright, DECADES) removed from the annual task of 'studying,' I still remember the secret to ALL wisdom. Know what you don't know.
This reflects in two ways upon my studying habit. First, I tend to ignore taking notes at the best of time. But I DO know where the holes in my knowledge are AND I don't kid myself that I know more than I do. If I don't know something, I admit it to everybody, including myself. Then I go find somebody or some resource that does.
Frequently, that resource is a textbook (or, in my continuing learning case, a manual or a case study). Now, I tend to OWN most of those materials and students don't always have permission to mark up THEIR resources. But if they do, here's my method for learning and retaining information from not-occasionally deadly-dull reference material.
Go through the text highlighting everything you DIDN'T know in yellow. There will be lots of yellow. At least for most of us. And when I say, “didn't know.” I mean DID. NOT. KNOW. Most of us have a peripheral knowledge of lots of stuff. I'm currently reading Jack Horner's How to Build a Dinosaur. If I was studying this 165–page book, it would look like yellow foolscap. The small amount of white left over is NOT a credit to my academic upbringing. At least as far as biochemistry, biophysics and other things bio, including biogeochemistry.
Some time later (say the night before you take the test about whatever you were reading), go through the reading material again … IGNORING ANYTHING WHITE. You are only interested in the yellow stuff. Take a pink hi-liter and mark all the things you STILL DON'T KNOW, turning the hi-lite orangish. The next day, you will review the orange sections and see if there is STILL stuff that isn't sticking. Those, you hi-lite with a blue hi-liter and you will get get a purple-hued section.
This latest scanning and colouring is NOT for suddenly retaining this information. Just tracking down the orange sections you didn't know will serve that purpose. Nope, the purple sections are for the end-of-term exams which are frequently MONTHS after you did the original studying.
When you do get to that final exam and are looking to speed your studying methods, you can make a decision as to whether to start with the remaining yellow, orange or purple sections. Me? I tend to start reviewing with orange. I can frequently reconstruct my missing yellow-level facts from the orange and purple ones. And there's some subjects where all I would do is look for purple.
By the way, there is one more colour level: Brown. Created by applying a green hi-liter over the purple sections. Brown means you've read the material (or part of it) FOUR times and still didn't retain that knowledge. At some point, you just have to surrender to the fact that some subjects are unknowable.
Like women. They REALLY don't like being painted on with hi-liters. Trust me.