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Take rest. The biggest factor affecting concentration is rest and this has been approved by research. Concentration requires your mind to be calm. But your mind will be scattered if you are not well rested. Make sure that you get the right amount of sleep at the right time. Also have regular sleep time, and this can be the key step for concentrating.
Sleeping too much is also not ideal. Oversleeping disrupts your natural rhythm and can make you lazy. Avoid this by having an alarm clock to wake you up in time.