Dear first of all dress nicely.
2ndly be confident and positive during interview.
U will be asked questions in following order.
Introduce urself
why u want to join this department?
Some questions related to ur last degree,on whose basis u applied for said post.
Then questions related to current issues of Pakistan and world.
Good luck 4 ur interview.
Do share ur experience in this forum,because I m also waiting 4 my interview of Asf inspector.
All the very best
Regards
Mansoor Ali