Making your old guitar strings(bottom/thick strings) sound fresh again to make it sound Bright/"Twangy"/"Grindy"/"Snappy"/"Djenty" or whatever you describe it.
I've watched a facebook video before, it's actually for bass guitar tips to make pop and slap sound alive again, but I still gave it a try and it works!
Just loosen the string about 6-8 half turns, then pluck hard the loose string for about 10x.
Tighten and tune the string, repeat the steps for the remaining bottom strings.
There you go, muddy string tone is gone.
Note:
1. It doesn't apply to higher/unwounded strings, just wipe the dust and rust, you don't want to break it.
2. I suggest you plug and listen first to your guitar before doing this to appreciate it more.