The absolute, number-one, most important thing to remember when playing live music in front of an audience is this:
The very best way to get more people to repeatedly come out and see your band play live is word of mouth. When your live shows are great, people will like it and talk about you to their friends both online and offline. Besides the obvious point of playing good music that people like, there are 5 main areas of preparing for your gigs.
1. Your individual playing
The most important thing you can do (individually) to prepare for your gigs is to focus on playing your songs 'consistently well'. To improve this, practice your songs in a wider variety of environments and situations. Play your songs standing, walking, in the dark, under a strobe light (if you have one), while talking, without looking at your guitar, while friends are listening, etc. The key point is to practice playing consistently well in all those different scenarios. This will help your individual performances on the stage.
2. Your band's performance
When your band rehearses, you should NOT be focused on playing the songs correctly. If your band mates cannot play the songs flawlessly BEFORE the band rehearses, send him/her home to learn the songs. Once he/she has truly done that, then bring that person back to band rehearsals. Band practice is not about 'holding people's hand through the process of learning the songs which should have been learned at home. If you have a band mate who needs your help learning the songs, you can do this by meeting alone with that person to help. However, if this is a consistent problem, then you may need to replace that band member for someone who is better (or less lazy if that is the case).
Band rehearsals should be about the band playing the songs TIGHT rhythmically, matching dynamic levels in various parts of the songs and developing great stage presence (more on this later).
Because it can be very difficult to really know how good your band is in any of these areas as you are practicing, I strongly suggest to record your band rehearsals in 2 ways:
Video record your rehearsals. When you watch the video, turn the volume OFF and simply pay attention to how the band looks visually. This will help you to really focus on the stage presence and visual impact your band may (or may not) have on your next audience.
Audio record your rehearsals. Do this with computer based recording software and make sure each instrument is recorded onto its own track (multi track record). [Do NOT listen to the audio from the video recording!]. The first thing to do is LOOK at the recording on the computer screen. You want to notice patterns of rhythmic flaws. Is your bass player always playing slightly before the beat? Is your guitar player playing slightly behind (late) the beat? For many people it is much easier to 'see it on the screen' than it is to hear it. Once you see it, then you will be able to hear it afterwards much more easily. Doing this exercise will really help your band to play much tighter rhythmically (which is absolutely critical for any band). Also listen to how the dynamic levels of the band are changing? Does everyone get louder and softer at the same time? Or is everyone doing their own thing randomly? It almost always sounds best when the band does this together.
3. Your stage presence
When you play live, your music is only 50% of what most people in your audience care about. The other 50% is what they see. Remember, they came to 'see and hear' your gig. Great 'sounding' bands often lack bigger success because their live shows suffer from lame stage presence. If you want more people to consistently come out to your gigs, you must develop great stage presence.
As mentioned above band rehearsals aren't about 'learning to play the songs.' Schedule at least 50% of your band's rehearsal time to analyze your stage presence skills (watch the video as described above and take notes on what you notice), then begin to implement improvements to this part of your live playing. You can make a lot of improvement on your own simply by some self analysis. If you want more help, check out my free stage presence tips.
4. Eliminate (or at least reduce) stage fright
If you have cool music, a cool band and have prepared well to give your audience an awesome show, that can all be quickly destroyed if stage fright gets in your way. Many musicians simply don't perform well on stage due to anxiety. Don't let this happen to you and your band. You have worked too hard to let fear cripple you. Your audience deserves better, and more importantly, YOU deserve better! You are on stage to have fun, not to be nervous every moment of the gig. To eliminate (or at least to significantly reduce) performance anxiety, check out this stage fright article.
5. Performance logistics
In addition to stage fright, there are other things that may happen during your gig that can hurt it. The main two issues are not being able to hear and not being able to see. If you've already played gigs, then you know that every gig sounds different on the stage. One night you can't hear the bass, the next night you can't hear yourself, etc. When you are the opening band, you typically don't get a sound check before you play, so you have no idea what you will be able to hear (or not hear) on stage until you start playing the first song. While there are many different ways to deal with this problem, I'm going to focus only on one of them here. One of the best ways to prepare for not being able to hear all the instruments is to practice your songs with you and only ONE other instrument. So for example, practice playing only with the bass player. Next, practice the song only with the drummer. This will prepare you for live situations when you can only hear the bass or only hear the drums etc.
The next common logistical problem is not being able to see. Often live stages are dark in some moments and then extremely bright in other moments, making it very hard to see your instrument. My eyes are very sensitive to light, so I always play with dark sunglasses on (since the bright lights often blind me on stage without them). For dark situations you can add white out (or even glow in the dark markers) on the side of your fingerboard, so even in very low light you can clearly see your fingerboard. Of course practice playing the entire song without ever looking at your guitar is also a great way to prepare for unexpected lighting problems on the stage.
My now Globally Revered, Multi-Award Winning One Man Band has been around since 1992, when I finally got plenty weary of "baby-sitting" other musicians and singers!
I am blessed with a 5-1/2 octave voice (natural & falsetto combined) I play both Rhythm and Lead Guitar simultaneously.
I kick midi bass pedals, and have written natural-sounding percussive parts for every one of the 2500 Songs I perform.
I also have a keyboard that I have re-invented to follow my artful guitar work. all I have to do is select the sound effect I want for each tune!
I also have a studio quality vocal harmonizer that I can selct the age, nationality, style, etc for 1 to 4 backup singers that must follow my voice and/or guitar upon command!
Hence, I sound like 8-12 musicians and singers in my LiVE "Golden Oldies Review!" Concerts and Shows.
My point is this: No matter what your act is comprised of, practice, practice, PRACTICE! I record and video my rehearsals and performances, ever evaluating my artistry, appearance and professionalism, for every little nuance is critical to my shows' success!