Hello,

At central level SSC CPO is conducted for recruitment of Sub-Inspector(ground duty)  in CAPFs, Sub-Inspector(Executive) Delhi Police and Assistant Sub-Inspector in CISF, the exam is conducted in four phases, the first phase has four papers namely general knowledge and general awareness, general intelligence and reasoning, quantitative aptitude, english comprehension. The second phase has only one subject English, now coming to the  booklists for each subject;

English Comprehension: Wren and Martin Grammar Book, Norman Lewis's Word Power Made Easy, SP Bakshi's General Objective English is good for practice.

General Intelligence and Reasoning: RK Agarwal's Verbal and Non-Verbal Reasoning or MK Pandey's Analytical Reasoning

General Knowledge and General Awareness: Read newspaper on a daily basis to cover dynamic portion, Lucent's GK is good for static portion.

Quantitative Aptitude: RK Agarwal's Quantitative Aptitude for Competitive Exam, Arihant's  Fast Track Objective , M Tyra's Quicker Maths.

Apart from this, there are many competitive exam sites where you'll get practice paper, so use them they will help you a lot.