[OMFG!You'reActuallySmart!]

I'll start off by saying I'm only taking science classes, so it may be different than for non-science classes.

I find it to be quite helpful to read the assigned chapters after the lecture because some things can make more sense or explained in a different way. So I prefer to read after the lecture when everything is still fresh in my mind. When I'm reading and something clicks giving me the "AHA, eurika!" moment, I write it down in the textbook margins so when I'm studying for a test, I just look at my scribbles.

On the other hand, I read before the lecture when I look at the slides before the lecture (some profs post slides before the lecture) and the slides confuse me. I turn to the textbook hoping it can clarify it because I don't want to just write down every word the prof says, I want to write down a summarized coherent version and it's easier to do this if you have some understanding of the content before-hand. For example, yesterday I had a lecture in my course of clinical audiology and I didn't quite understand the slides the prof posted the night before, so I turned to the textbooks (this course has 2 books). After reading, I had a better understanding but still a bit unsure on a few things. Happily, the prof explained those during lecture.

When I'm reading after the lecture, I make note of the things that prof AND book state because that stuff is likely to be more important than some obscure reference. Keep in mind, the prof may not explain everything from the book because they may spread it out across lectures and profs don't often follow the exact order of the textbook. Some profs also have openly stated they wanted us to figure it out on our own and they'd just get us started in the right direction each lecture. That can be a bit frustrating especially when the prof says a bunch of stuff that's important but not in the textbook. I had several profs like that, particularly for a third-year course in neurophysiology and electrophysiology. I found it was useful to stick around after class or go to their office when my group or just I was completely confused. As long as you showed effort, the profs helped.