If you'd like a salt rim, run a lime wedge around the rim of your glass then dip the rim in coarse kosher salt. Set the glass aside until ready to use.
In a cocktail shaker or mason jar, combine the tequila, fresh lime juice, orange liqueur, agave nectar, and some ice. Optional: add a splash of orange juice.
Shake vigorously for 5 seconds.
Taste the margarita for sweetness. You can add more agave nectar if you prefer.
Strain the margarita over fresh ice into your prepared glass. You can add a lime wheel, wedge, or twist for garnish if you desire.
Notes
If you're making a pitcher, combine all ingredients and add 1 cup of ice. Stir until the ice has dissolved, then keep refrigerated until ready to use. Pour over fresh ice.
My recommendation for the most affordable, widely available, and additive-free tequila, is El Tequileño. Any tequila brand you prefer is perfectly acceptable- drink what you like!