Don't cycle with a headphone or earpiece.

Good tip! It is really dangerous when you cannot hear the traffic around you.
I do like to listen to some up-tempo music when I go cycling sometimes, but I know the dangers of not being able to hear the other traffic. That is why I bought a 'bone conduction headset'. This is a headset you don't put in or over your ears, but it rests on your jaw bone. This way you can both listen to music and hear everything around you.