Plug all instruments into an open input on the audio mixer using either 1/4 inch or standard XLR cables. Each instrument will have its own channel on the mixer.
Adjust input levels. One at a time, ask each musician to play his or her instrument. While they play, look at the level meter on the appropriate channel. Make sure the instrument is not "clipping." You will know the instrument is clipping if the clip indicator lights up or the level meter begins to turn red. You want the signal to be as close to the red clipping level as possible without exceeding it. To adjust the levels, simply turn the gain knob left to make the signal weaker or right to make the signal stronger.
Raise volume levels. Once input levels have been set, raise the volume fader for each channel until you have a good basic mix of all instruments. Make sure that the combined input of the various instruments does not make the master output channel clip or overload. Clipping on the master channel is indicated in the same manner as the individual instrument channels--the clip meter will light up, or the level meter will turn red. If this occurs, turn the volume down on one or more of the individual instrument channels on the audio mixer.
Adjust the EQ. Once you have a good mix, adjust EQ settings on the individual instrument channels. The EQ knobs are usually labeled lo, mid and hi. These settings will allow you to adjust the frequencies of each instrument.
Add effects. Use the FX send knobs to add effects like reverb or delay to individual instruments. It is common to add reverb to a vocal, or a delay on a guitar or drum channel.
Turn up the master fader until you have reached the appropriate listening level for the venue you are working in.