Your password should never be the same as your ID.
It should never contain your first or last name or other personal information (date of birth, nickname, license plate number, pet names, friends).
It should never consist of common variants and repeat/keyboard patterns, such as asdfgh or 1234abcd.
Your password should not be too short. Use at least 10 characters.
Use lower- and upper-case letters, as well as symbols or numbers. The symbols and numbers should not be at the beginning or end of the password string.
When utilizing umlauts (ü, ä, ö), keep in mind that you may not be able to enter them on keyboards in other countries.
Avoid words that appear in normal dictionaries.
Using words that are spelled backwards or creating them with so-called leetspeak (replacing letters with similar-looking numbers or symbols) is not a good way to create a secure password either.