Always check the balance of your props. The only props I've found that need almost no balancing are the Zinger woods. The simplest balancer is basically a short rod that fits neatly through the prop and has pointed ends to hold between two fingers. The trick is to hold it as lightly as possible so it doesn't quite slip out of your fingers.

HOW to balance is another thing though and everyone has their own opinion. First thing of course is to get rid of any moulding flashing (including at the tips). Then check the balance. If it's out then the first thing to do is sand off any paint (if any) from the heavy side. From there on, make up your own mind how you want to go. Personally I sand evenly over the entire curved surface of the heavy blade. Now for the other opinions