1. Have Confidence in urself but dont be over confident
2. Watch a lot of BBC, CNN , Geo and stuff.
3. they always ask u about ur hobbies so be well prepared about it.
4. u should be well versed with ur optional subjects , u will be asked a lot from there.
5. try to be patriotic and never criticise the government in a harsh way.
6. u should be well acquainted with the geography of pakistan.
7. they might ask ur views on important national issues like NSC, LFO Democracy etc.
8. They can also ask u about the economy of pakistan.