A long "password" can be achieved by using a sentence, which is typically easy to remember but also sufficiently complex. Not a jumble of words like the horse battery staple, but a real sentence. It is easy for people to use sentences that apply to their own lives but are not at all easily guessable. For instance "Fluffy eats too much bacon."
One problem with this approach though is that many apps or sites don't allow spaces, or they have the counterproductive 'policy' that forces you to use a number, a special character, blah blah blah, but only allows some small number of characters. But it works great for modern OS passwords. So go ahead and set your policy to length only and advise users to make a sentence.