How to choose a good password
Some security experts recommend using a password based on a mnemonic, such as an easily remembered phrase. For example, take the first letter of a each word in a phrase, then add a few special characters or numbers to it. For example, "lend me your ears" can become "lmye4%" (maybe even including the quotes!). "To be or not to be, that is the question" can become "2Bor!2b?".
Of course, having seen these examples in a widely publicized document, do not use them literally.
This is good technique, but you may need some patience to think up a new phrase every time you change your password -- especially if you have to think of a different password for every system that you log into. This may lead some users to recycle some version of their old password - another security threat.
Another easy way to choose a good, safe password is to let an application generate a random one automatically. If you can use the same password on multiple systems, then it's only one random string that you must remember. If you use it a few times after setting it, it will be much easier to remember.
Password Manager makes remembering passwords easy by synchronizing passwords, so that you only have one password to remember, and that password works on every system and application.
Password Manager can provide a suggested list of randomly generated passwords, and reject passwords that do not comply with strong password rules, so that you always choose good passwords.
When to Change Your Password
Perhaps just as important as how to choose a new password is when to do it. New passwords are most easily remembered if you start using them immediately, and use them often. Don't change your password at the end of the day, the end of the week, or before a holiday. Instead, change your password in the morning, at the start of the week. Your mind will be clearer, and frequent use of the new password will reinforce your memory.
Always use a new password a few times after setting it!