Use a different password for every account.
If you are using the same password, or obvious variations of the same password, on each site you login to, then your password is only as safe as the site that gets hacked next.
If you use only Apple devices, then iCloud Keychain does a great job of suggesting good passwords and storing them securely for you.
Once you are ready for a little more — like sharing some passwords between members of your family automatically, I recommend a good password manager, like 1Password or LastPass. These tools will help you manage changing your passwords regularly, inform you when a password is leaked, and more.