Bring the main sliders down to the minimum position before plugging anything into the mixing console. This will prevent any sound damage from occurring when microphones and other instruments are plugged in. Doing this will allow you to keep all the other sliders in their positions, as some mixing consoles have 48 channels and pulling down all the individual sliders would take much longer.
Plug the microphones and instruments into the mixing board. Each channel will have one or more inputs you can use, depending on whether you have a balanced or unbalanced signal. Microphone cables provide a balanced signal, while an instrument cable normally is unbalanced. Label each channel and place them logically in groups, such as all the drums together and all the guitars together, as well as the vocal microphones.
Adjust the trim knobs on each channel, as well as each individual channel slider of the mixing board. The trim knob is a quick-adjust gain knob that should be set to allow enough signal to the channel as to not distort the input. Adjust the slider to the 0 point first and slowly adjust the trim knob so the signal is just below clipping to provide a strong signal to be recorded or amplified.
Adjust the EQ on each channel while the instruments are being played. Solo each channel to hear how it sounds and make all of the necessary adjustments based on the overall sound of the group and in reference to the other groups of instruments as well. A perfectly EQ'ed channel when solo may no longer sound good when mixed in with the other instruments.
Slowly bring the mains up whether you are using the mixing console for a live show or for recording. These sliders send the mixed audio to the main output as a stereo mix, so pay careful attention to the pan settings on each channel as well. Many guitars are panned left or right, and some drums are also mixed in this manner. Bring the stereo mix to just below clipping for the strongest signal without distortion. Remember to adjust these sliders during the show when the instruments get louder or softer to allow the audience to hear all that is going on during the show.