First and foremost of importance is that you start reading dawn Newspaper Opinion section daily. dont spend too much time (not more than 30-45 mins) on Newspaper.
This Habbit will not only improve your English (Grammar, Sentence Structure, vocabulary), but also help you with Essay writing and current affairs.
Get New College Composition as it is a good book.
for everyday Science, get your hands on Kashmiri's book (General Science and Ability)
For Pakistan Affairs, there are many books, some of which are follwoing:
Struggle for Pakistan by I H Qureshi
Towards Pakistan
Pakistan Affairs by Mohsin Raza
Constitutional Development by G.W. Choudhary
For Islamiat get Islamic Studies by Shazia Ramzan
Introduction to ISlam
Islam the misunderstood Religion
Islam At at Glance
All these steps should help you with your Preparation