Whenever possible, when trying to learn a melody or song words, I try and listen to the piece ten times in a row without noodling with any instrument - just active listening.   

Then, if it's a song, I either type it out or write it out long hand.

A good place for me to work on memorizing words is in the shower, for some reason that seems to be a place I can focus well. I have read that some studies show actors memorize words best while lying down (?)