One trick is to use the first letter of each word in a phrase or rhyme - for example, the first two lines of Humpty Dumpty become ''hdsoawhdhagf''. Make some of the letters upper case, drop in a few symbols and you've got the foundations for a secure password.
When creating a wide range of passwords you might want to start with a strong base password such as HdSoAw*70. From that you can generate unique passwords for different services, such as gHdSoAw*70m for Gmail and fHdSoAw*70a for Facebook. Make sure your pattern isn't so simple that if someone discovers one password they can easily guess the others.
Source: The Brisbane Times, Technology, by Adam Turner, 7 June 2011.