As an added measure of security, include symbols over alphanumeric characters in a password. Symbols are special characters, accessed by holding down the Shift key and pressing one of the number keys (0-9) on the keyboard. There are many more characters, which, if used, can make an even stronger password. To access them, hold down the ALT key and press any combination of numbers on the number pad (number keys at right hand side of the keyboard).
Another advantage of special symbols is the ability to use personal information to some extent without others being able to decipher the password. For instance, "I.WaS.BoRn.@.ElM.StReEt" is much more secure than simply "elmstreet" or "I.was.born.at.elm.street" This allows creating easy to remember yet difficult to break passwords.
Finally, besides making an unbreakable password, it is a good idea to change the password every 30 days or so.