Should I start preparing by directly following the study plan?
 

One should start the preparation directly by following study plan or 1st he should read & learn a full course & then for revision he should follow the study plan ????????????????

It totally depends upon the availability of the time and the aspirant's know-how of the subject.
Anyhow, it is better to follow the study plan. Read the highlighted topics in detail. When you are able to cover the topics highlighted in the Study Plan, you yourself will be able to exclude or include any other topic. It is better to view the Past Papers at that stage and include and cover the remaining topics.