The key, to me, is not MEMORIZATION, but "Dum-ditty"---that is, get it in your head so you can dum-ditty it while you're doing something else. Listen to it over and over and over, until you're almost sick of it. For me, memorize does not necessarily mean learn. I can memorize a concerto, but not a "tune". I even managed to forget 2 bars of "Redwing" and HAD to go back to the paper to re-learn it! I use a combo of both paper and ear, but ear is better for really learning a tune.