This is a common question many people have when they start learning songs. It's not as hard as you think to sing and play your instrument but it does take time, patience and practice. John McCarthy gives some insight on how he first started to sing and play guitar.
John says "it is hard to sing and play at the same time, I know because I went through a transformation from Guitarist to Guitarist/Vocalist and it took some time and practice".
"Here's what helped me through the process. I learned the guitar parts first because they were a little easier for me to master, then I memorized the lyrics to the song so I had it down cold!! Next I would try to walk around the house playing the song without paying attention to the guitar. I would try to talk to someone while playing the song or watch TV while I played. You must make sure that it becomes second nature to you".
Another tip John has is, "Try singing the song from different sections then than the beginning, like start singing at the second line of each verse. This will allow you to have the song totally in your memory bank.Then I would try to combine the two parts, it still won't be easy at first. However, it will became less difficult every time you start a new song and then all of a sudden it will be second nature".
Be patient everyone has the same hurdle to jump and the biggest stars had to go through the same process you will go through!
You can get more tips from John McCarthy at www.rockhousemethod.com