Connect all sound sources to the amplifier or mixer using the respective audio cables. Make sure all audio input and output levels are turned all the way down. Label all audio input channels by applying a small strip of masking or gaffer's tape on each input channel and writing the name of that audio input source, for example, "vocal" or "guitar."
Connect all sound monitoring devices to the amplifier/mixer. Arrange speakers away from microphones to prevent audio feedback noise.
Set all active audio input and output levels to "0" or "U," "unity."
Test the audio levels of all input devices by performing a sound check. Start playing any prerecorded music, speak into any microphones or play a few notes or chords on any musical instruments. Listen to the sound check using headphones, if desired. Adjust audio levels and equalizer settings as needed to achieve the desired sound mix.