Three rules to follow when backing up a Bitcoin seed phrase:

Keep your seed phrase offline: Your seed phrase is the key to your Bitcoin wallet, so you should always keep it offline and in a safe place. Avoid storing it on any device connected to the internet, such as your computer or smartphone, as this makes it vulnerable to hacking and theft.

Store your seed phrase in multiple locations: While keeping your seed phrase offline is important, it's also important to have multiple backups in case one backup is lost or damaged. You could consider storing your seed phrase on a piece of paper or metal, and keeping copies in a fireproof safe, a safety deposit box, or with a trusted friend or family member.

Keep your seed phrase secret: Your seed phrase should only be known by you and trusted parties. Avoid sharing it with anyone else, including strangers, friends, or family members who may not have your best interests at heart. Additionally, avoid writing down your seed phrase in a way that could be easily discovered by others, such as leaving it in plain sight or in an unsecured location.