Chill glassware if desired: Coat the outside of a glass with water and freeze until serving time. Or, freeze dry glassware for 2 to 3 hours before serving.
In a cocktail shaker, add gin, lemon juice, and simple syrup. Fill shaker with ice, cover, and shake until outside of shaker is very cold, about 20 seconds.
Fill chilled glass with ice, then strain cocktail into glass. Top with club soda and garnish with a skewered lemon wheel and maraschino cherry if desired.
Notes
Glassware: Collins glass is a tall, thin, straight-sided 12-ounce glass.
Simple syrup: Combine equal parts granulated sugar and warm water (ie, 1 cup sugar, 1 cup water) and stir to combine. Cool completely.
Vodka Collins: A cocktail made with vodka instead of gin.
Tom Collins with grenadine: If you like a sweeter drink, float a little grenadine on top.
Rum Collins: Use rum and either lemon or lime juice.