[starsailor]

I agree with all the comments above, and think that Johnnydox's comments about getting those lyrics memorized is important even if you're not doing it live, when you play the tune you can hear those lyrics and figure out where to put them in a song, also break the song down, sing a verse over and over to get the hang of it and slowly piece the song together once you have the first couple of verses and the chorus down you've virtually nailed the song, the biggest problem is timing doing the chord changes and making sure your voice varies with the chord changes that's the thing that takes practice, it also depends what key your voice is in some of us sing high some of us sing low etc. not all songs suit our voice so that has to be taken into consideration as well, all singer songwriters originally write songs to suit their voice so the songs have to be reworked to suit whoever's performing it, I sing quite high so I don't think there's much chance of me singing old man river in the near future without bringing the keys up a bit.
I also sing songs at every opportunity without the guitar, singing makes you feel good, I think everyone should do it irrespective of how good their vocals are, it's good for your health