First of all you should know the syllabus of SSc Chsl and exam pattern then according to that make your study plan and work on it..cover all the subjects, since you never know which subject will be asked for more marks..Mostly 70% – 80% of the paper is based on the theoretical concept. Hence, you need to focus more on knowing the basic theoretical concepts..Make short notes while preparing for the exam. This will help you to revise the topics that you have covered. and at the last try to attempt online mock test to know where you stand and how much you prepared for the exam...