first of all, plan what you wanna do for the day. put it on a planner like google keep or tasksboard. once you are done with that particular task, tick the checkbox. take a quick break (maybe 5 mins). get back to doing the next task. don't do anymore than 4 hours of studying a day during the weekdays in year 11 (maybe increase that to 5 in yr 12). spend time with your fam, go play a sport, watch something you like. don't exhaust yourself by just studying the whole day. this will keep you motivated to study the next day.
Extra tip: May take a quick power nap once you get home from school and then start studying. this will help you freshen up (works for me, not sure about anyone else)