The teacher told us to study hard and not waste time.
Tips
grammar
Set verb-object phrase. 抓紧 (zhuājǐn, literally 'grasp tightly') means 'to seize; to make the most of (time)' and pairs naturally with time-pressured activities: 抓紧时间 (make the most of the time), 抓紧工作, 抓紧训练.