Always use the power button when turning the printer on and off.
Check that the power light is off before you disconnect the power cord.
The ink itself can dry out if it is not covered. Just like placing a cap on a fountain pen or an oil pen to prevent it from drying, make sure the print head is capped properly to prevent the ink from drying.
When the power cord is unplugged or a power outage occurs while the printer is in operation, the print head may not be capped properly. If the print head is left as it is, it will dry out causing nozzles (ink outlets) to clog.
In these cases, turn the printer on and off again as soon as possible to cap the print head.