Northern-

I believe you said you were singing unaccompanied. In that case you probably need to be a lot closer than 12 inches from the mic, depending on how loud the song is. In my case, assuming the mic is similar to a Shure 57, I'd sing a ballad about 3-4 inches from the mic, and a loud shanty 5-6 inches from the mic.

It is also important to stay focused on the mic with your mouth, not wander about from side to side or up or down.

The sound manager should be your friend. Ask him or her what would be best for you.

Cheerily,
Charley Noble