When you make a note of your password, always write down which application, service, website etc the password applies to. Make some notes when you have to produce a password for the first time about why you needed it.
I notice, when asked for a password, many novice IT users are not sure which password is required so start using passwords they have listed instead of working out which password they need.
Passwords are like bunches of keys, you need to know which one will open the right door. However, if you keep trying the wrong keys, the door owner will disable the lock.