Maybe reward yourself whenever you accomplish a certain task? Or maybe if you find things satisfying when they are complete, there's an app called adapt which fills up when you have done all the subjects (its a good app for organising as well). Study how long you want to as long as its effective revision. If you want you can start as early as you can when the first lessons start but I wouldnt stress yourself out and just get into a habit before thinking about having a plan of hardcore revision, if this makes sense