This is a constant issue. Passwords are easier to guess than most people think, so it is important to choose passwords that are not guessable.

1. No dictionary words or names. It is possible to  use a phrase as a reminder, but there are lists of common words, even if you tack a couple numbers on to them that will cut the time needed to locate your password down considerably. I have found lost passwords in a couple hours.
2. User longer passwords, more than 10 characters.
3. Use numbers, upper and lower case, and non alphanumeric characters.
4. Don’t use the same password on multiple systems. Someone may take your password from another system and use it to log in to something more important.
5. Change the password quarterly.
6. Don’t reuse old passwords.