Before you start studies, do a general overview of what you have to cover. How broad or how narrow are the topics you need to be familiar with and what time do you have to cover all these topics before the D- day.
Then try and divided your work at a pace that will help you. For example, you may decide to cover one topics or subject per week, or per day or per month accordingly. This is where timetable comes in; draw a good timetable that will ensure that all topics or subjects are included. This will help you not to omit any subject. If you read randomly and not with timetable, it is very likely you will focus on some subject and starve other subjects of your attention.
In conclusion, a good timetable make studying very systematic and organised.