That's the approach I follow in my projects.
I offer a Javascript (window.crypto powered) Diceware passphrase generator and use zxcvbn to let users know the relative strength of the password they've supplied.
I've also been planning an experiment to see if the width of a password field results in users choosing longer passwords, because more empty space. :)
I'm going to use the appeal to authority argument, and bring over Schneier to argue that writing your passwords down isn't bad: https://www.schneier.com/blog/archives/2005/06/write_down_yo... (and others posts since, google "schneier writing passwords down" or something)
Remembering your password isn't necessarily more secure, especially since it easily leads to password re-use, which is even worse.
If you enforce all kinds of weird password rules to the user, he will have to write the password down somewhere, because one couldn't possible remember all passwords. And for non-technical users that means some random pieces of paper or post-it notes. On the other hand, encouraging them to come up with something that is strong makes it more likely that they will invent a password that they can remember, thus making it more secure.