Put the gin, lemon juice and sugar syrup and a few ice cubes together in the shaker.
Shake very well, as this is the only way to create the frothy crown of gin fizz. You don't have to be afraid of watering down the drink, as it will later be filled with soda water anyway.
Then strain into a long drink glass filled with ice cubes.
Top up with soda.
Garnish with a lemon wedge or something else that suits the gin's taste.