How to backup bitcoin private key?

Best solution: print ten copies of the mnemonic when there is no camera and you have only yourself with you. Put them in a plastic bag to keep them dry. Keep them in a safe place.If possible, you can also laser etch them on the stainless steel plate.

The next best solution: you can copy them manually, be case-sensitive, and keep them neat. To be careful, you can copy them twice and store them in a plastic bag in a safe place.

Other networking situations, cloud storage or stored in the phone album are likely to be lost or stolen.