Your seed phrase must survive two dangers at once: being lost and being found. Storing it well means balancing both.
Against loss
- Keep at least two copies, in two different places.
- Protect them from fire, flood and accidental throwing away.
- Make sure someone you trust could find them if something happened to you. You will study inheritance at the Master level.
Against theft
- Never store the phrase next to the hardware wallet it unlocks.
- Do not label it "bitcoin seed" in plain sight.
- Tell as few people as possible that you own bitcoin at all.
Common good places
A home safe, a safe deposit box, the home of a trusted family member. There is no single perfect place: what matters is that one disaster or one burglar cannot both destroy all copies or find one.