Use a different password for each of your important accounts like email and banking. If you use the same ‘key’ to lock your home, car and office, then all of them are compromised if a criminal gains access to one.
Writing down your passwords is not necessarily a bad idea because it is surprising how many passwords an average person needs to remember. Just make sure that it isn’t in plain sight. Also, don’t forget to change these passwords regularly.
Use a combination of numbers, mixed case letters and symbols. You should also consider using a phrase that only you would know. Just in case you do experience a ‘senior’ moment, set up your password recovery options and keep them up to date.