Protect your password
Never share your password with anyone, not even a colleague or relative. If another person has your password, they can, for all computer purposes, be you. This extends far beyond simply reading your email. This could include sending email as you or gaining access to sensitive financial or health information.
It's very important to use different passwords for different systems. This limits the damage a malicious person can do should a password fall into the wrong hands. Everyone understands that it's nearly impossible to memorize a different strong password for each service you need to log in to. It's a good idea to have a set of four or five very strong passwords that you use on different systems.
Do everything you can to memorize your passwords or, instead, use a password safe (Keepass, LastPass, etc). If, for some reason, you absolutely must write down a password, always keep the note with you or in a locked file, and do not write down the corresponding username.
Six Great Password Managers