I strongly believe slowing it down does the trick. It worked for me with Wild World and most recently Rock-n-roll Hoochie Koo. I will play the song at a snails pace and sing. The tempo will come to you. This worked very well for me with Rock-n-Roll Hoochie Koo. Last night I was doingt he riff to Rebel Rebel and started to do the vocal no problem. That would have been almost impossible for me before. I could strum and sing ( Working Class Hero etc) but never a riff or notes and sing. Now I am getting it. If you need to start strumming chords and singing fine. Pick a Beatles song and just strum slowly and sing. Even if it's sung with a riff just play the implied rhythm chords and sing, It will come to you.