Tom & Barbara Brown do a festival spot called 'Making The Song Your Own'- I'll leave them to explain how! For myself, I lose the instruments and learn the tune and words simulataneously by singing them out loud until they're pretty well fixed, then try to fit the guitar or mandolin around them. Otherwise you're stuck with the thrum or technique of the instrument rather than the voice coming through as imho it should if a song's words are truly the focus...