First, it’s harder to recall things when you haven’t slept. Second, sleep strengthens the bonds between brain cells that help you remember for the long term. Third, it’s harder to form memories in the first place when your mind is wandering because of a lack of sleep. Good “sleep hygiene” can help: Shoot for 8 hours a night, exercise daily, stick to a regular sleep schedule, and avoid alcohol and caffeine late in the day.