Stay focused on one thing at a time and don't get scattered. Much of this depends on whether you enjoy what you do. You also need to get enough sleep and eat well. Active brain function requires a lot of energy. I personally take brain supplements for better concentration. The brain likes to be taken care of.
Try to get enough sleep (not always working), try to remember that being less productive from time to time is ok (not always working as well), using daily planners