There are many threads regarding this. Many seniors recommend current affairs by safdar mahmood and contemporary affairs by imtiaz shahid. However, I have found their quality to be deteriorating.

Here is my strategy: Reading the newspaper is a must (not all of it but editorials, main headings, etc.). Use the internet to research topics (very important). As current affairs is such a vast subject you will need to identify which topics to research. For this use current Affairs by Rai muhammad kharal. It contains events for the last few months which is extremely useful to identify important topics for the examination.