At work I have to use several passwords:
Network log-on, which periodically tells me that my password will expire in 14 days and would I like to change it now? Why? If it needs changing tell me to change it, why ask me if I'd like to do it 14 days in a row?
Oracle log-on
Oracle upload form log-on
NHS Supply Chain log-on

And outside of work:
Web-mail
Instructables
various others

Password security can be important, some systems will annoy you by insisting that your passwords are (this long) and alphanumeric, and "no you can't have that one because you already used it in the last 365 days"

They do it because poor passwords can be a security risk

Here is a short guide on how to choose good passwords, and remember them

Step 1: Pick a Password

I spent 11 months crunching invoices for a large chain of builder's merchants. Every day I'd see the same ten alphanumeric account codes: they're long enough, alphanumeric and meaningless to virtually everyone else on the planet. These I use for my network log-on.
If I need to remind myself of which one I've just changed to I only have to write down one of the alpha characters.

Many years ago Viz comic published this top tip:
"Save money on expensive personalised car number plates by simply changing your name to match your existing plate. - Mr. KVL 741Y"
For the Oracle log-on I use something similar (you know your own licence plate yes?), the "Mr" can be changed to "Mister", "Mrs", "Junior" and again you can remind yourself which one you're using with a simple note that tells you which member of the family it is.

NHS Supply Chain gave me an easy-alpha numeric, I just change the numeric. E.g. if you use 1234, next time use 5678, you only need to write down the first character if you know your own sequence.

For passwords which don't need changing I use an alphanumeric combination of addresses I used to live at a long time ago. If I need a reminder I use a city name.

Main points:
Use something that is alphanumeric
Something that is of particular significance to you
That is beyond guessable / non-dictionaried
(I knew a Kiwi who used Maori words)
Something that you cannot forget or can easily remind yourself of without revealing it

Step 2: Don't

-use your girlfriend / boyfriend / spouse / child 's name.
-leave passwords lying around
-share them with anyone
-write all of them down on a piece of paper / notebook which you keep on your desk
-add all of them to an Office document named "passwords"
-use terribly simple passwords like "password" or a repeat of the username