Best way to memorize, or rather not forget, a passphrase is choosing a passphrase that only you can dig up instantly from your memory because you have special appreciation for it's origin. Could be a line from a song or poem, a quote from a movie or a line from your favorite book.
Guilty pleasures are a good source too since nobody probably knows what they are.
Poems, songs, lyrics, lines from books ,avoid those.
Dictionary attacks will break your passwords pretty fast.
It has to be random stuff.