If you already don't have them, get a decent recording device and a good microphone. Start recording yourself playing and singing. There is no better way to see exactly what you have to work on.

First of all, I find my recorded voice sounds very diffrent from what I hear in my head. That is a big adjustment. When the tone can ring in your skull, what you hear is not what your audience hears. So get used to that, because it is what your listeners hear that you need to craft.

Once you make that passage, you can start to objectivly evaluate...what to focus on keeping and what to work on improving. Once again, what you experience when you are working to play chords and remember the words and keep the rthyum and the pitch and the tone and still not trip over the gum you are chewing... All that... has nothing to do with what what your audience experiences. So now you can start to objectivly work on HOW YOU REALLY SOUND.

Recording also allows you to record the guitar part. You can practice the singing, without playing the guitar. This allows you to really focus on THE SINGING. You can put them together when you have the both firing on all cylinders. Much easier to master the use of your vocal cords when the guitar part isn't distracting you. Vocal performance is all about attention to small, vocal details. Recording makes it possible to break the process down to managable parts.

I find that vocals are the hardest part of peforming a song. If I have to sing, it is imperitive that my mind is completly engaged with the singing. I promise you that people will notice your voice going flat before they notice that your B string is flat. (Even if all you can think of is that damn b string.) In the final annalysis, you have to get the vocals right if you want to ever have an audience.

At least this was my experience and I have seen if work for friends who were developing those skills as well. Recording and reviewing, in a very real way, was where we all found our voices. It is not an easy thing to do, but that brutal reality is the direct route to what you seek to master. Just remember that the traveling of that journey, I[u]S THE GOAL[/u].... not some imaginary, preconcived, point in time and space.