You know you should back up your data, but some lesser known maintenance tasks also play vital roles in keeping your Mac running fast and smooth.

Task Schedule
Check for updates with Software Update Automatic setting
Back up with Time Machine Automatic
Defragment (Micromat TechTool Pro/Prosoft Engineering Drive Genius) Once a month
Repair Disk Permissions (Disk Utility) Once a week
Delete Unnecessary User Accounts (System Preferences) As necessary
Scan for viruses (Intego VirusBarrier X6, ClamXav 2) Automatic
Check all volumes for errors (Disk Utility/Micromat TechTool Pro) Once a week
Check for the latest drivers for your hardware Once a month (or after installing new hardware)
Delete temporary Internet cache files (Prosoft Engineering Drive Genius) Once a month