1) Place some salt on a small plate. Rub the rim of a martini glass or rocks glass with lime (reserve lime for serving); dip the rim in salt on the plate. Fill with ice and set aside.
2) Combine tequila, triple sec, lime juice, and simple syrup in a cocktail shaker. Fill shaker with ice, cover, and shake vigorously until outside of shaker is very cold, about 20 seconds.
3) Strain cocktail into the glass. Garnish with a lime wheel and enjoy!