The smartest way to use previous year question papers is to solve them under timed, exam-like conditions and then analyse every mistake, not just read them. PYQs show you the exact pattern, the repeatedly-asked topics, and your real weak spots, which makes your revision far more targeted.
Start once your syllabus is mostly covered. PYQs are a revision and testing tool, not a way to learn a topic for the first time. Cover the basics, then bring in the papers.
Solve them like a real exam. Sit with a timer, no notes, and complete the paper in the actual time limit. This trains your speed and exam temperament, not just your knowledge.
Analyse afterwards, deeply. This is where the real gain is. Mark which questions you got wrong and why, which topics repeat year after year, and where you wasted time. Revise those specific areas before the next paper.
Spot the patterns. After a few papers you will notice certain chapters and question types appear again and again. Those high-frequency topics deserve the most revision time.
Example: A Class 12 student in Pune solved the last ten years of board papers, kept a list of repeated questions, and focused her final revision on them. Many similar questions appeared in the actual exam.
One practical tip: Keep a small repeated-questions notebook as you solve PYQs. By exam time it becomes a goldmine of the most likely questions, far more useful than re-reading the whole book.