Rim a glass with salt or sugar by dipping the rim in lime juice and then into the salt or sugar.
In a shaker, muddle the fresh strawberries until juicy.
Add tequila, grapefruit juice, lime juice, and simple syrup to the shaker.
Fill the shaker with ice and shake well for about 15 seconds.
Strain into the prepared glass filled with fresh ice.
Top with club soda and stir gently.
Garnish with a strawberry and a grapefruit slice.
Serve immediately and enjoy!