Accompanying yourself in performance can be a blessing or a curse, depending on your skills at each of your instruments. For my part, I've never considered myself either a great singer or a virtuoso guitarist. If you're like me, and I know I am, the artistry happens in the magic somewhere between the two.
It is a schizophrenic challenge to learn to play an instrument in more than a "boom-chick" fashion and sing at the same time. It's like skiing. When you're first learning, you are very busy concentrating on your poles, your skis, centering over your feet, looking down the hill, bending your knees, and the myriad of suggestions you receive from all the people who are better than you. In reality though, when it all comes together, you're only doing one thing—skiing. Same is true for the apparent duet of accompanying yourself. You are plinging. (Sorry.)
A couple of years ago, I injured my hands and was unable to play. I found to my shock, that when just singing, I couldn't remember any lyrics to my songs! I discovered that to remedy the situation, all I had to do was hold a guitar and just kind of "thub" along and it was all there again. Weird.
Essentially, the thing to do is learn how to stay out of your own way, so you can concentrate on what you mean. That's what mastering your technique enables you to do. Incidentally, there is a marvelous little book called Mastery by Kelley Wilde (Dell Publishing) that would tell you much more about this than I could hope to.
There are some inherent problems presented to guitarist-singers (or pianist-singers). Many performers, in order to hit their higher notes, have to sing louder than they can play, and as a result they overplay the guitar, ruining their sound, adding buzzing, and breaking strings to their repertoire. This seems to be true with amplified acoustic guitar as well. The tendency to overplay is still there, I think, because singing is more athletic than playing. It's difficult to teach your body to do two different dynamic things at once. It's like shooting hoops while typing. Keyboard players can have the reverse situation, feeling like they have to sing louder than they want to, to keep up with the dynamics of an instrument three times their size. Everyone is different in this regard, but a natural balance between singer and instrument is rare. At the very least, not paying attention to the difference will severely limit your dynamic range.
As a result, when I'm asked to do a show really acoustically, that is without a PA system, I gracefully pass when possible, and bring along a little sound reinforcement. Without it, I find I both sing too loud and play too hard. Truly a non-musical experience.
All this, of course, assumes that you know something about getting a good PA sound. It is an art of its own, beginning with learning how to use a microphone. Here's a word or two about them: If you're too far away or if your distance from the mic is constantly changing, you have a problem. You have to give your sound person and sound system some volume and some consistency to work with. So get closer and stay there. Not too close, though. If you keep getting your mustache caught in the wind screen, or you receive that occasional invigorating shock when your lip touches the mic, you are too close. They call the resulting sound "proximity effect." It is a boominess, a false, "clubby," lounge kind of sound, comprised of the equalization properties of the microphone rather than the true sound of your voice. A little is nice. Too much is not.
Some mics are kinder than others with regard to proximity. A good one is the Shure SM-58; an honest sounding and virtually indestructible mic. There are many other good mics, but I mention the SM-58 because it is the workhorse of the industry, used by every sound company. The mic costs about $100.
The guitar or piano for self-accompanied performers can be used in very effective, almost orchestral ways, paying attention to bass parts, inner voicings, melodic harmonizing with your vocal and many other elements. This also makes it possible to screw up in rather flamboyant ways. As I mentioned in my first article, one-person-bands tend to overplay, oversing, tune sharp as they blast onward and rush the time. I find myself habitually playing through a passage that should, for example, be simple struck and allowed to ring. I think that we get so used to singing with the guitar supporting us that we're insecure without it. It's difficult to remember to do just what the song needs and no more. Also, I'll find myself playing too busily because the notes are just laying there under my fingers, and it's too tempting, or I'll just like the way my hands feel or something stupid like that. Occasionally it takes the sobering playback of a live tape to teach me, once again, to be true to the song.
A grasp of the value of dynamics can be among the last elements to arrive in one's artistry. It is a hell of a lot more important than getting louder and softer. Create a kind of dynamic map in your mind before you begin the song. With it, you can really be effective where and when it is more important. If you start your song without this kind of foresight, you become the victim of your starting volume, tempo, attitude, etc. It's really worth remembering because you need to leave yourself somewhere to go dynamically, without topping out on either instrument.
It's a great feeling when it all comes together. You finally get to the place where you relate the voice texturally with your guitar. Your vocal intonation instantly improves, and you seem to know more about where to place your voice "between the strings" as it were.
OK. Once you have the fundamental performance down, instrumentally and vocally, then you'll automatically begin to develop little variations—a vocabulary of options, which you can use without going too far out on a limb. (Improvisation starts with getting out of trouble well!) It allows you your changing moods in different situations, and also to keep your material fresh for yourself after repeated performances. Be careful though. There is the danger of becoming flippant by taking liberties with material that you've maybe done too long. If you're adding this and that just to keep yourself interested, maybe it's time to "simple up" and go back to the real meaning. If you find yourself thinking about fixing your car while doing a particular ditty, maybe it's time to retire the song. Hell, maybe it's time to go back to dental school. Nah.