It's not so black and white, and it depends on the class for me.
For instance I pretty much just read through my circuits book of everything we're going to cover that week and that's it.
For quantum I do the same thing but then before my mon/wed/fri classes I reread the material relevant to what we're covering on those days as well as reread it after class and take my own notes - if I'm struggling I'll work through some of the problems that were not assigned for hw.
Oh and by read, I mean reading for understanding which usually includes a lot of pauses during the process to think about what is actually being said.
The one thing I always do without fail is reading lecture material before going to the lecture. I can't stress enough how important this is. By going into a lecture with familiarity of the subject I get a lot more out of it. In my opinion, lectures should be less about gross learning and more about clarification of difficult concepts. Of course this is not a perfect world, so for a majority of students most of their learning takes place by listening to lectures.
I study for every class every day (M-F; I usually do very little studying on the weekends unless I have multiple upcoming tests or papers to write). On a normal day I will independently look over upcoming lecture material during the morning then go to lectures. After class I will review what we just covered along with previous material that will appear on the upcoming exam. Honestly, this equates to about 3 hours a day of studying. The advantage here is twofold. First of all, I never stress over examinations or have to feverishly cram for them. I just show up and the information flows from my pen. Secondly, I retain the information for a much longer period of time. I still remember most of the things I learned in my freshman year as a senior. This is great not only for future reference but cumulative finals are much easier. I take reading notes every time I read. This is crucial to retaining information. A professor I had during my sophomore year said to treat college like a job. Work from 8-5 every day and enjoy your weekends. Since doing this college has been magnitudes easier and more beneficial for me.