Sing as much as you can to strengthen your voice. For each song you sing there is an optimum key that will suit your voice, find it. Remember that if you're performing in public, especially acoustically, the key you feel comfortable with while singing in the house may not project. Try it a bit higher and keep your head up so you're hitting the back of the room. So many people come along to sessions and seem to be singing, head down,to the back of their guitars - result, mumble, mumble.