Air Gapped OpenPGP Key (New Wiki Entry)
It is recommended to first quickly read this article from top to bottom without taking actions. After you roughly understood how it’s supposed to work, re-read this page and do it step-by-step. Exercise this with test keys first. If that works, consider doing this with your primary keys.
Make backups of your existing GnuPG files ($HOME/.gnupg). Keep them safe. If something goes wrong during the following steps, you may need this to return to a known good place.
You should know how to boot other operating systems than your primary every day operating system from Live DVD and/or other external media such as USB.