Having a huge number of codes is not necessarily more secure - a single multi-application, one which you have in your head, is better.

Have one code for highly sensitive purposes, such as bank accounts, and one that other people might eventually share for getting in and out of buildings and documents.

Use your basic code and an unvarying principle for making up new codes. If you need an alphanumeric code, take a favourite line from a song and use the first letters of each word.

Try to use a word or acronym that has a pronounceable sound.

Try not to use birthdays, which thieves can easily guess. Think of something equally memorable, such as your age and your partner's age.

Hacker folklore says the most used passwords/PINs are birthday dates, "password", "secret" and "qwerty". So much for our rich inner lives.