How do I stay productive ?

Im getting a lot more than before but sometimes my productivity wavers in the day. Sometimes its hard for me to stay concentrated on my school work or any kind of work I need to be doing. How do you guys stay productive and discipline and motivate yourselves ? I have one of those whitebpard calendars and I’m thinking of hanging it up to write down all my assignments and their due dates because it’ll help me stay on task everyday. What do you guys think??