Pre-Partition syllabus of Pakistan Affairs according to the new syllabus revolves around 'Ideology of Pakistan'. Now Pakistan Affairs feels more like current affairs. A candidate needs to firm his/her grip over contemporary issues of Pakistan and proceed in a way that nourishes his/her analytical skills.
Preparing 'Ideology of Pakistan' portion is not kind a hard nut to crack. You may consult any standard level book for this. The real challenge lies in other parts of the subject.
For this make daily newspaper (preferably Dawn) and Monthly edition of Jahangir's World Times' study a regular part of your routine life.
Pakistan Affairs by Dr Usmani and Liaqat Niazi
Political and Constitution History of Pakistan by Hamid Khan