Good after none everybody;

I am an English lit. student and tomorrow I have Proficiency Examination.

My question is about the usage of possessive ('s) and (of). I just cannot find a general rule to know when to use the ('s), the (of), and when I use non ?

and I also want to know if there any tricks to pass the Proficiency Examination; I have to write a 500 world essay in 2 hours

Thank a lot