Rim a double rocks glass with salt and fill it with ice.
Pour the gin and grapefruit juice into the glass and stir to combine.
Garnish with a grapefruit wheel and fresh herbs, if desired.
Notes
To rim a glass with salt:Add a few tablespoons of kosher or flake sea salt to a shallow dish.Wet the rim of the glass by running a wedge of citrus along it. You could also fill a separate shallow dish with grapefruit juice and dunk the rim of the glass in the juice.Dip the moistened rim into the salt and gently shake to remove any excess.