In your class, add your club soda. Some recipes call for this as the last ingredient, which it can be if you want to fill your glass up or add more of the bubble making stuff.
In a shaker, combine your gin, juice, simple syrup, and egg white. Shake this for a few seconds. Maybe 10 seconds or so.
Now add ice to your shaker and gin fizz ingredients, and shake some more, a bit longer this time. Maybe 30 seconds or so.
Strain and pour your gin mix into your soda water.
This drink doesn't have ice in the finished product, so your glass may have room for more soda on top if you like.
Skip the garnish and enjoy the egg white moustache.