If you know in advance that you will have to miss a class, you might schedule an academic activity outside the class, or ask a colleague to cover for you. If the decision to cancel class is sudden (due to illness or another emergency) you should notify your students as quickly as possible. You can contact them via email through GullNet by opening your class roster and hitting "contact all." In addition, if at all possible you should contact your department administrative assistant during regular business hours to request that a sign be posted in the classroom notifying students that your class is canceled.