Measure your stage and audience area and make a clear diagram of them. Make sure to note the actual size of each area on the diagram. Mark where you will set up performers in your most common situation. This will be based on the type of venue. A church setup will be very different from that of a nightclub that typically hosts rock bands. Whatever your setup is, note where you will place performers on the stage most often, as this will determine how you need to place your stage monitors.
Place the stage monitors no more than three feet from where the performers will be. Ideally, stage monitors will be placed seven feet to 10 feet from each other on stage. If your stage is not that large, you may want to get more than one musician to use a monitor. Try to do this by type of instrument or musician's duty. Group singers together and those who play percussion instruments together if you must get musicians to share monitors. If you have an extremely small stage, you may need to set up only two monitors at the front of the stage for singers and one in back for the drummer.
Make sure the stage monitors are angled no more than 45 degrees toward the listening area. Having the stage monitors pointed more toward the audience than that will cause the mix between the house and stage monitors to become very muddy and unclear.
Keep the house monitors pointed away from the musicians on stage. The same 45-degree-angle rule applies to the house monitors. Pointing them too much toward the band will make it impossible for the band to hear their individual monitor mixes.
Try to keep stage monitors pointed away from walls as much as possible. Sound waves will bounce off hard surfaces and go into the audience area. This will make the sound muddy, and in some cases can even cause a time delay between what the audience hears through the main monitors and the sound bouncing off the walls. This can make for a very uncomfortable listening environment.
Use a separate mixer to control the house and stage monitors. This will enable you to get rid of feedback caused by stage monitors very quickly during a live performance by simply lowering the stereo faders on the monitor mixer. Having a separate mixer will also allow you to quickly adjust overall stage volume between bands or performers.