Spamming is also a much hated e-mail practice. Some spammers like to send out a message to 20,000 people in one go. This is most inappropriate. Normally spammers are promoting dubious products, get rich quick schemes and pornography, but often the budding entrepreneur thinks this is a good way to get started with Internet Commerce. Avoid forwarding jokes to eveyone you know.
Chances are they have already seen it.
Avoid sending large attachments to heaps of friends. Send this to 10 friends and you've just despatched 50MB of worthless crap over the Internet. The same goes for XmasGuy and XmasGirl and any other meaningless rubbish. Try to prioritise your use of this valuable resource. Generally e-mail messages cannot contain a virus however any attachment you receive can.