I keep a general timetable of extra tasks to do each week, generally an hour or two of tasks each night in addition to weekly to do lists.
Mine for example,
Monday- French practice paper (which takes 3 hours, but monday fun)
Tuesday- 1.5 hours of HSC practice maths questions
Wednesday- 1 academic article for E1 english and 1 for advanced to be read/annotated
Thursday- 2x Practice multiple choice sections for economics on BOS website and 1x short answer section on something we have already done (i should probably ass essays this year though)
Then I do those tasks first as they're the 'optional' tasks, so my to do list each week homework/test revision/writing notes/vocab lists which is obligatory will definitely be done afterwards. If i did it the other way around, I think I would rarely do my extra tasks as there is no one making me do them and I would lose energy.
personally, the mixture of a set schedule and one that changes week-to-week works best for me.
If you plan to do a set study schedule, I would recommend having set tasks to do in each time slot, for example, not just "do bio study" because you will end up spending some of the time figuring out what you will do, so it would be better to write "make bio notes" or something like that.
Hope this helps and good luck!