• Write down you private key on a paper and store it in a secure location.
Writing private key manually isn't good idea, because
1. It's easy to make mistake (such as skipping a character or write wrong character) when you write the private key due to the length.
2. Importing it isn't exactly easy either, sometimes you need to convert the format (e.g. HEX to WIF).
However, there's no major problem if you're writing the seed or print the private key.