Diceware is an easy way to create strong passphrases, still easy to remember.
Introduction to diceware - Wordlist in use.
Diceware uses a dice to create random sequences from a list of words, and ensure the password is usable. However, computing random is an issue. This prototype runs with PHP, which introduces random_int() in its version 7. To provide larger compatibility and get free from the PHP version, random_compat (on GitHub) is used.
A string between 4 and 6 words is generated at every refresh. For each and every word, a random integer is chosen between 0 and 1, deciding if the word comes before or after the existing string. Once the maximum amount of words is reached, the string is outputed.
Please note this is a prototype in order to provide a basic approach.