After every dive

• Rinse the regulator in fresh water with the dust cap on and the first stage dry — don't press the purge while rinsing
• Soak and rinse the BCD inside and out; drain it fully
• Rinse your computer and check the battery indicator

On a schedule

• Service regulators per the manufacturer (commonly annually or by dive count)
• Replace computer batteries before long trips
• Cylinders need periodic visual inspection and hydrostatic testing — check the stamped dates