Don't be an unintentional spammer
You may get messages from friends, warning you about a new virus, health scare, charity appeal, or con trick.
These are very likely to be hoaxes or just plain wrong. Be very suspicious of messages that ask you to pass them to "everyone you know". What should you do with the next one you receive? Delete it! Why, you ask? Because chain letters and hoaxes have the potential to cause problems (lots of network traffic or just filling up someone's inbox) and they can also be very annoying.