Ok, let's see if I can remember enough to be of any use here:
In high school, I believe I graduated with somewhere around a 3.8 or 3.9 gpa. As far as studying went, the only time I actively remember doing anything even remotely resembling it occurred for my 9th or 10th grade history class, which required a great deal of reading. Beyond that, I would generally look over the material for a few hours the night before an exam. I also remember one particularly slack-ish moment where I walked into AP Physics my senior year without realizing we had a test that day.
All in all, very little studying was done in HS.
As for undergrad, I studied more frequently, but it still largely consisted of over-nighters. The only classes for which I can remember actively and regularly reviewing ahead of time (and keeping on top of my homework) were Organic Chem and Bio.
All that's definitely changed in grad school, though. I now spend my weekdays, weeknights, and weekends reading. Basically, anytime I'm not in class, or popping into some kind of non-academic activity for an hour or so to keep my brain from imploding, I'm reading. And I'm loving it.
In summation: I didn't study much throughout HS or undergrad, but in all honesty, I truly wish I had. I also have the utmost respect for anyone who does. Getting good grades doesn't mean a damn thing if you don't remember any of the material a week after taking the test.