Backing up GPG keys is quite simple, but easily forgot (for me). Just put it a notes to myself on how I back it up and restore it.
To export keys and its owner trust
gpg --export --armor YOUR_ID > YOUR_ID.public.asc
gpg --export-secret-keys --armor YOUR_ID > YOUR_ID.private.asc
gpg --export-secret-subkeys --armor YOUR_ID > YOUR_ID.sub_private.asc
gpg --export-ownertrust > ownertrust.txt
Optionaly, you might want this to cancel your pgp keys if you lose private keys
gpg --output YOUR_ID.asc --gen-revoke YOUR_ID
To import keys and trusts
gpg --import YOUR_ID.public.asc
gpg --import YOUR_ID.private.asc
gpg --import YOUR_ID.sub_private.asc
gpg --import-ownertrust ownertrust.txt
To make it ultimately trusted (optional)
gpg --edit-key YOUR_ID
gpg> trust
Your decision? 5 (Ultimate trust)
3