Provide the stage mix soundboard with the same audio signals the front-of-house mixer receives. You can most often accomplish this task by using a special multicore cable called a snake that not only provides a central location for connecting microphones on stage but also splits the signal so two mixers can be supplied.
Choose only key elements to transfer to the stage mixer, including all vocals and instruments such as guitars and keyboards. If you do not need electric bass and drum microphones hooked up to monitors, group these instruments together on mixer channels to the side of your main channels, or do not connect them to the stage soundboard at all.
Check to determine how many monitor mixes you need. If you are using a stage mixer, you may find it easy to provide, within reason, each musician with his own mix. For a four-piece rock band, for example, you can direct four auxiliary feeds to four amplifiers (or two stereo amps) and on to four monitors.
Adjust the auxiliary levels to provide a rough mix to each feed, then request input from each musician to fine-tune the individual monitors. Generally, vocalists prefer to hear more of themselves in their own mix. Rhythm instruments may be next in importance to keep everyone in time. The stage mix engineer is equal parts technician and diplomat.