How to Mute Unused Strings on Electric Guitar
Unmuted strings are the main source of extra noise on a distorted tone (see [[playing-clean-with-distortion:the article on playing with distortion]]). Muting isn't one technique - it's both hands working at the same time, each covering its own zone of strings.
The picking hand: palm at the bridge
The edge of the picking hand resting near the bridge (the same move as palm muting - see the dedicated article) mutes the strings below the one currently being played - the ones physically closer to the hand. That's the main defense against the thicker bass strings humming.
The fretting hand: fingertips resting on neighboring strings
Fretting-hand fingers not busy holding the current note lightly rest on neighboring strings - usually the higher-pitched one - not pressing them to the fret, just deadening their vibration with light contact. This especially applies to the finger that just released the previous note: instead of lifting fully off the neck, it stays lightly touching that string, muting its ring.
Both techniques work together, not in turn
The picking hand covers strings below the note being played; the fretting hand covers strings above it and behind it in time. Together they cover nearly the whole neck - neither technique alone handles every noise source, so it's worth drilling the combination, not each hand in permanent isolation.
Drill: deliberately compare with and without muting
Play a short pentatonic phrase (see the article on getting started improvising) first with no muting at all - listen to all the stray noise. Then play the same phrase while deliberately applying both techniques, and compare. The difference is usually bigger than it sounds like it would be before trying the exercise.
Over time it becomes reflex
At first, muting requires conscious attention to both hands at once, which feels like an overload. Like any other mechanic (see the article on speed and cleanliness), it gradually becomes muscle memory - after a few weeks of regular playing, the hands start muting stray strings automatically, with no separate command.
Try it in practice
Open chord trainer