Begin before you learn to read is the best way. Too late for most people now with the availability of song-books. In the 1950s I reversed the learning process with reading when I was given a small song-book of Christmas Carols. I was about four years old and already sang hundreds of songs learned by ear. I taught myself to read using that book and the Stephen Foster song-book my father had.
Songs I learn from books remain a visual memory of written words. Songs learned by ear are tied to images within the song. I try not to write a song down until I know it by ear.
Joy