For strong memorable passwords, use phrases.
Longer is better. If there's no character limit then tell a 1-2 sentence story, something secret that only you know. All lower case no spaces. A 100 character password is going to be really hard to brute force even if the attacker is operating on the assumption that you only used lower case letters.
It's also pretty easy for you to remember if it's a phrase about a secret personal experience.