Use a 8 x 11 mini groundplan, and mark which wing, in which direction you want the monitor facing. (Is it for singers to look at from the stage or backstage chorus or soloist to look at or hear.
What kind of monitor should be indicated: visual of conductor/ audio of orch/ or both
Act/ Scene and time
Since electrics usually do this, you might want to turn this into an Elecs plot, with any smoke/fog/pyro effect placements, any electrified practicals on and off set, any twinkly candles or candleabras, etc.