AOA madam there is alot of material on the internet to prepare this topic completely. For theoretical understanding of the topic go to wikipedia, google any source, You can read Chapter 4 from Goldstein's book for this purpose but here comes the tricky part. There are not high chances that you may get asked to enlist the determinants of foreign policy or subjective questions like that in the exam.

Instead you would be asked a question about foreign policy of any major state, it can be a question related to Pakistan too. So make your rreading vast, make it so vast that if you get any such question in exam. you are comfortable in answering it. Read the foreign policy of America, China, Saudi Arabia, Iran, India Pakistan, Russia the more you read on the topic the more you learn.

Hope it answers your question, surfing the internet in an intelligent way would do the trick.