I was an Olevel Islamiat Student and i gave my paper in 2011, god blessed me with an A+ in islamiat, my own experience says that try to learn as many quranic verses and ahadith of the HOLY PROPHET (pbuh) as you can on every topic in the syllabus. Quotations is the KEY to get an A+.
(1) ISLAMIYAT a core text for olevels (by, David R. Thomas and Mustafa draper)
(2) ISLAMIYAT (by, Farkhanda Noor Muhammad)
(3) O'LEVEL ISLAMIAT (by, Iftikhar ul Haq and Maulavi Jahangir)
(4) ISLAMIAT (yearly) Redspot
(1) Marking Schemes (click here for all marking schemes)
(2) THIS WEBSITE PROVIDE ALL NOTES BY SIR IFTIKHAR UL HAQ