Start with Volume at unity (~5), Tone around 5–6, and Sustain 7 for a thick singing lead. Because the Muff has scooped mids, keep the Tone from going too dark if you play with a band so it does not get buried.
Why does my Big Muff disappear in a band mix?
The Big Muff has famously scooped mids. Nudge the Tone control brighter (past the midpoint), reduce the Sustain slightly for more definition, or place it after a mid-pushing pedal so it cuts through.
Recommended starting points are community-researched estimates — every pedal, amp and guitar is different. Dial from here, then GuitarToneAdapt helps you match a target tone on your own rig. Pedal comparisons · Amp settings · All tones