i'v seen too many of those who always think max gain/max dist/max overdrive/max presence = better (emphasis on metal/rock/punk). So learn how to use those knobs to make the best out of ur sound & tone. What's worse, sometimes the bass is too much..boom overtakes the bass guitar, which results in excessive boom factor. It sounds like SRS WOW effect thrown to the max in WMP.
Next - this applies to lead guitarists - never be selfish. Always adding in your own fills (like what has been already mentioned) and excessive soloing may not be better afterall. Now, the biggest factor - maintaining the speed and tempo. If ur the type that has passion for hyperorgasmic racing, u bttr know how to control. Be courteous, you have been warned.
Tuning, like what others have also mentioned, is a major problem. Don't b ignorant when it comes to this. If u have a floating-bridge guitar, depending on the quality of it (how it retains the tuning), make sure to do it before u go for ur session. If ur guitar is lousy like mine, always check before going in to the studio. Being a perfectionist & tuning to the dot (like how u would leave ur answers to a mathematical sum to 6 decimal places) may help in critical situations, like recording.
Effects. According to how u want ur tone to sound like, it may be wise to plan & mix well, that is if u do mix. Look for the right type of sound. Same applies here like my first para, dont overdo anything unless ur sure its required. Too much here n there may contribute to ugly sounds.