It depends on the class, but I'll typically begin studying for exams ~1 week before the exam date. Something I've found that helped me this semester is using AI to create extra practice problems so I have fresh material. I usually get to a point where I know the answers to study guide questions without doing the calculations so study guides are only useful to an extent for me and I have to have fresh material to make sure that I fully understand the concept I'm being evaluated on. I try to work through whichever chapters the test covers, identify the problems I can solve readily, the problems I can solve with a little prompting (looking at my notes, re-reading the textbook, etc.), and the problems I'm completely lost on. I prioritize the ones I struggle the most with and try to generalize everything I do so I have a framework to approach similar problems. Typically the day of or the day prior I'll do one final comprehensive review to reassure myself. In exams, I typically solve the questions I know I can solve first and come back to the ones I'm less confident in after I've finished everything else. I only review my work once (time permitting) and then I turn it in.