If you're reading this you may be wondering either "Let's see what this Am has to say" or "Let's see this guy make an ass of himself". This is my first article and please read it with an open mind and don't just flame me at the end of it.
Common Mistake #01: Too loud or too much gain - So you are getting ready to play your set in a club with your first band. You turn on your amp and tune at a low volume then you crank the amp's volume and hit the distortion. The audience shouts and covers their ears as you strum your first chords suffering from painful overloads on their ears.
Solution: First thing to do turn down the volume! You may have a 400 watt half stack but you don't need to use all of it. Especially not in a club that is probably no bigger than a basement. You will drown out everyone but you and the performance will suffer because of it. Not to mention the audience doesn't always enjoy being slammed with a wave of ear-piercing feedback and speakers nearing the tearing point. If the drums can't be heard over you, turn way down. This is what soundchecks are for, get a band member to walk to the end of the hall and based on what he hears either turn up or turn down the Gain, or Volume. Too much volume/gain will cause uncontrollable feedback and no one will enjoy the performance except you. Also for tube amps the gain will be maxed at about 7 or 8, for solid state try and try again to get a good sound.
Common Mistake #2: Distortion Mistakes - You go to an audition for a Metal band and the sounds you get are overdriven tones reminiscent of Sublime. Or you get a british distortion going while trying to audition for a hardcore band. Or during your performance no one can hear that there are two different parts.
Solution: This goes without saying match sound and tone styles with the music. Meaning don't get a grunge tone going for a hard rock song, and don't slam on the ultra channel for a country rhythm. Also if the other guitarist has a British sounding distorion go for a more scooped out sound not too much you don't want to scrape rust off the heating pipes in the building. Of course scooping the sound isn't always the best option try a less gainy sound there are doezens of different ways to change the sound. If you do this then the different distortion will make the riffs sound thicker, and people will know there are two guitarists.
Well this is a couple of basic guidelines for tone and sound characteristics. Of course this is a trial and error part of guitar playing do what works best for you.