Have you advanced in your guitar playing to the point that you're performing for others? Maybe you're interested in playing at a local open mic event, or are ready to do a solo for a school or church concert. Or maybe you're part of a band that has jammed and practiced and is getting itchy to do some real entertaining. Whatever the case, there are some things to remember when you start performing for a group.
First, make sure you have practiced the songs you want to do until you know them inside and out. Nervousness will creep in and you will forget what you thought you had embedded in your soul! Get those songs nailed down as well as you can. Drill yourself on those chord changes and tricky rhythms until they are second nature. Rehearse any lyrics you might sing over and over. Don't bomb out just because you have failed to put the practice time in.
That said, be aware that technical difficulties can ruin an otherwise stellar performance. There is nothing unprofessional about taking a minute to check the microphones and monitor to make sure things are going to work for your particular brand of music. If you get started pouring your soul into a song, but the people can't hear you, or worse, you can't hear your own voice, it's going to throw your confidence for a loop.
A third consideration, touched on in the paragraph above, is to plan to pour your soul into your performance. When people come to hear someone make music, they want to feel the excitement the musician feels about the music. It's an intimate experience for the musician, and the audience wants to get in on it. If you are too concerned about the impression you are making on the audience, you will not be attending to the music like you need to.
Here's another consideration. Is the place you are performing noisy? Is it filled with people talking, laughing, and doing their own thing? Maybe you're in an active night spot, or performing for people at a fair. These people have other interests going on as well as your performance. The best thing you can do is lose yourself in your music. Don't worry about trying to drown out the noise. In fact, sometimes if you quiet down and have your own personal music party going, the crowd will quiet down to see what's going on on the stage.
The bottom line in performing is that how you look or impress the audience is not nearly as important as how you sound. Remember, too, that you don't have to prove anything to the audience in most cases. They are not sitting in judgment on you, but rather are hoping you do great. They'll likely feel sorry for you if you flub a bit and will cheer if you pull it off. So don't look at those folks as someone to impress, but someone on your side.