how can I manage my time

it's a very important time, so you should manage your time for the best study in boars you do work with a very systematical way like
Make a proper timetable in which you have to set a full day schedule.
Daily you have to study the main subjects for at least 2 hours.
before doing anything set your aims or priority to achieve your goals.
use a calendar and mark the important dates like test dates, exams dates.
so, if you try all these things, you can easily set or manage your time or easily score good marks.