See the thread of "yesterday" titled: Help: Learning songs (click)

Here's an excerpt I wrote in it, and a lot of the other comments in that discussion go with your question. If you are going to join that thread you might indicate that here so others will know where you are looking for replies to your question.

--------------------------------------------

Sometimes once I think I've "got it" I will play the recording more and more softly as I sing with it. At first I am following the vocalist on the recording, but as it gets softer and I can barely hear the words to it--I find I am leading and then making it my own. That works well for words and melody. You can also whistle, the brain seems to like it and recall it well.

Sometimes it helps to see the printed music and see how the tune is constructed rhythmically, or see what melody phrases repeat. Once you see how it's built, it's easier tor recognize the sections and instinctively feel the transitions. It's like going for the same walk every day, turing the corner to see a familiar sight.

Then, once you've lived in the neighborhood awhile, you just go, without even thinking where or how. In the song, you stop being so conscious of the "bricks" it's made of and you can focus on the unique features of the day. Like when you turn the corner and someone has just painted their front door bright red since you last passed. I might be singing "Swing Low Sweet Chariot" three days in a row but on Monday I am in my car thinking about a sick friend who wants angels to take her away. On Tuesday I am in the kitchen doing dishes and I might be thinking about something else and spontaneously come up with whole new verses. On Wednesday in the shower I might find I'm in some kind of silly mood and the melody and rhythm might start sliding into a jazz/blues/swingy thing.

Which one will I do Saturday night in our church service? I don't always know. The versions will have added up to something fresh for that night, probably. I just let the song go ahead and be the song.

I think when people worry about learning a song they are worrying sometimes about doing the song RIGHT. That means doing it the way you haeard it or think it's supposed to be done. You think it can be perfect. It doesn't work that way. The song is the song and it becomes yours, and how you do it is how it should be done, that particular time. You only need to learn it well enough to let your mind and heart take it and keep it and share it. If you do that it will be different every time.

When you don't know a song, try doing it anyway. You might find your mind fills in a whole new melody, and if you can capture it you have just written your own new song. Sometimes my head will take off from Song A to somewhere else completely--- go into a nonexistient melody for awhile-- then end up in Song B. This is much more fun than learning how Doc Watson sings each note on his record. And the truth is, Doc only sang it that way once, it's never the same on the live album or in concert.