A piece of advice from Security experts:
Don't choose a password which is obviously associated with you. Hackers can find out a lot about you from social media, so if they are targeting you specifically and you choose, say, your pet's name you're in trouble.
Choose words that don't appear in a dictionary.
Hackers can precalculate the encrypted forms of whole dictionaries and easily reverse engineer your password. Use a mixture of unusual characters. You can use a word or phrase that you can easily remember but where characters are substituted, e.g. Myd0gha2B1g3ars!
Have different passwords for different sites and systems. If hackers compromise one system, you do not want them having the key to unlock all your other accounts.
Keep passwords somewhere safe. With multiple passwords, it is tempting to write them down and carry them around with you. Better to use some form of secure password vault on your phone.