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Practice good sleeping habits to keep yourself at your sharpest. Being well-rested helps you stay alert and focused. Additionally, your brain synthesizes information that you picked up during the day while you sleep, so a good night's rest will help you learn and remember things more effectively. To sleep better, make sure you:  Establish a regular bedtime routine. Go to sleep and wake up at the same times each day if you can. Keep your bedroom dark, quiet, and comfortable at night. Avoid using caffeine and other stimulants at least 3 or 4 hours before bedtime. Turn off all screens (such as your TV, computer, tablet, or smart phone) at least an hour before you go to bed. Spend at least half an hour unwinding before you go to bed. You might take a hot bath or shower, do some stretches, or read a bit of a relaxing book. Choose a diet that is varied and rich in healthy fats, green vegetables, dietary fiber, lean protein, and complex carbohydrates. These nutrients will not only give you the energy you need to stay alert, but can also improve the health and function of your brain. Try healthy options such as:  Fatty fish, like salmon and trout. Nuts and seeds, such as walnuts, almonds, flax seeds, or chia seeds. A variety of vegetables, including leafy greens, legumes (like peas and beans), and colorful vegetables like carrots, radishes, and sweet potatoes. A variety of fruits, such as apples (with the skin on), berries, and citrus fruits. Healthy carbohydrates, like those found in brown rice, quinoa, and whole-grain bread. Having a little caffeine—like a cup of tea or coffee with breakfast—can help you feel more alert and focused, and may even be good for your brain's health. Too much, however, can leave you feeling jittery, anxious, and ultimately less focused and clear-headed. It can also make it harder for you to get a good night's sleep. While most people have trouble thinking clearly after about 6 cups of coffee, people who are sensitive to caffeine may experience ill effects after drinking just 1 cup. Get to know your own limits, and use caution and common sense when drinking caffeine. This means exercise that is active enough that you might break a sweat or start breathing a little faster. For example, you might try walking at a brisk pace for half an hour, 5 days a week. This kind of exercise can stimulate blood flow to your brain, improve your memory function, and reduce stress and anxiety—all of which lead to clearer thinking.  Other good forms of exercise include swimming, biking, dancing, and playing sports like tennis or squash. Doing household chores that work up a sweat, like mowing the lawn or mopping the floor, also count. If you aren't used to exercising, work up to your goal of 150 minutes a week gradually. For example, you might start by walking just 5 or 10 minutes each day, then gradually increasing the amount of time by another 5 to 10 minutes a week. Even a few minutes of exercise now and then can help you clear your head and feel more energized.
Get 7 to 9 hours of sleep each night, or 8 to 10 if you're a teen. Eat foods that nourish your brain. Use caffeine in moderation. Do 150 minutes of moderate exercise each week.