I would recommend that if you're just starting out and have trouble focusing like me, spend a few days/weeks on each subject to figure out how you revise best, what you need a lot of brainpower for, is this effective for me etc.
And then in the last few weeks, either stick to a revision timetable (with revision tasks not just the subjects) or make a study tracker where you make a list of all your topics and complete them making sure to track your progress
Everyone's different so it depends on how well you focus and whether you know exactly how you're gonna revise but I'm in Y9 so don't quote me