How do I fix feedback from my guitar amp when singing on stage?

Start by turning down your guitar amp — most feedback problems come from the amp being too loud on stage, not the monitor mix. The amp bleeds into the vocal mic, creating a feedback loop. Pull the amp back to just above what you need to hear, then angle it away from the front of the mic. Build the monitor mix starting with vocals: cut below 100Hz and scoop around 200-400Hz, then boost 2-4kHz for clarity. Add guitar to the monitor only after the vocal is stable.