I got good at calculus when I started doing differential equations. I got good at differential equations when I started doing modeling and control theory. In general, you don't get good at a subject when you learn it in class; you get good at a subject when you work on the stuff one level beyond it. So yeah, if you want to be good at the class you're in, start studying for the class after it. This is definitely an effective method.

But then again, that's really difficult to actually do. For anyone who grew up surrounded by resources, that might sound like a really easy and obvious suggestion. "Just listen to the tutors your parents bought for you." But for the students who can't afford books for this year's classes, you might as well be telling them to "just grow wings and fly, it's not hard".

Me personally, I knew plenty of people who did this, learned a year ahead so they looked extra good in class. Most of them had parents who had PhDs, paid their rent for them, and explained what problems they were going to face far ahead of time. For the students who leave class and go to work to pay their own rent and then go back to campus to study and do research at night, this is not very helpful advice. Like so many educational "one simple tricks", the unspoken prerequisite is "just be born rich".