Reward yourself after you finish something! For instance, if you read a chapter of your biology book, eat some gummy bears. Or, if you finish all of your homework, play Overwatch or Doom because fuck yeah.
Find a way to reward yourself after you complete something. No, I don't mean write down one word, then hour on phone. That is NOT how that works people. After you finish a piece of homework or read a chapter of a book or something, reward yourself.