Fill a collins or highball glass with ice. Add gin, lemon juice, simple syrup and soda water; stir. Garnish with a lemon slice, adding an orange slice and cherry if desired.
Variations on this classic cocktail are limited only by the distilled spirits that you have available. Popular variations include the John Collins, using bourbon instead of gin; the Brandy Collins, using brandy, cognac or armagnac; the Michael Collins, using Irish whiskey; and the Rum (or Ron) Collins, using light rum.