1. Ride right and pass on the left - Just like driving on the road, the rule of the road (or in this case bikepath) dictates you ride to the right and pass on the left.
2. Announce your presence - When you prepare to pass someone announce your presence. If you have a bell use it. If you do not, yell out passing, pardon, excuse me, or on your left! This prevents someone from becoming startled when you appear out of nowhere in close proximity and helps keep everyone safe.
3. Lights Lights Lights - The more lights the better. However brighter might not always be better. While more lights add visibility and help illuminate your bike, brighter lights might actually be uncourteous. Some bike lights now approach the intensity of a spotlight. If you are riding off road something like this might be a good idea to illuminate your trail and pick a good path. On the other hand, you do not want to be "That Guy" on a mixed use paved bike path who blinds everyone by using an ultrabright headlight.