Plug in the instruments and microphones whose sound needs to be sent to the main speakers. Use Direct Injection, or DI, boxes for instruments such as electric guitar and bass and use microphones for vocalists, guitar amplifiers and acoustic instruments. Label each channel with the name of the instrument or vocalists so you are aware of what you are working with.
Adjust the main volume to minimum and slowly increase as channels are added and effects shape the sound. You do not want the main stereo outputs to distort, or clip, your power amps and cause feedback. The "mains" on the mixing board are the most important set of controls as they control the overall sound volume.
Set the gain with the trim or gain knob to maximize the signal to noise ratio on each channel that will be used. If you have the right amount of gain going to the channel, you can mix the signal properly with the slider and equalization.
Set the compression on each channel to control the peaks and volume spikes that may occur during the performance or recording. By compressing bass, kick drum and other less dynamic instruments, it will be easier to control the overall level of sound going to the power amps.
Mute the channels that are currently not in use; this may include channels that will be used later. This will cut down on the overall noise introduced into the system. By muting open microphones, you will also cut down on the possibility of feedback.
Adjust the equalization of each channel to give the instruments, speakers or vocalists a smooth, real sound similar to what people would hear naturally. Use equalization to adjust the sound based on the overall acoustic properties of the room itself.
Add effects to individual channels to accentuate performance, such as reverb on vocals and the snare drum and delay on guitar parts and tail-end vocal pieces.