Play tight in the early stages let the donks waste their buyin, hopefully you pick up a hand during that time and it's you that sits pretty with their chips.

In the middle stages it's crucial, as a mistake = bustout, so play careful but not scared if you think you have the goods ship it in.

Late stages is different for everyone me personally I aim for the win so when there is 4 people left in a 9 man I bully the stack below me so if i'm 2nd in chips I raise the person 3rd in chips blinds and try and make a read and reraise him when I think he is weak. I do this because I feel that the person in 3rd feels he has more to lose than the person in 4th or 1st.

Obviously poker is not just black and white but with a basic approach like this you can't steer too far wrong.