First, prepare your citrus juices. Roll your limes and oranges firmly on the counter to maximize juice yield, then juice them until you have the required amounts. Strain the juices to remove any pulp or seeds for a smoother mix.
In a clean pitcher or bowl, combine the fresh lime juice and fresh orange juice. Add the cooled simple syrup and the pinch of salt. Stir everything together thoroughly.
Taste the mixture. If you prefer a slightly less tart or less sweet margarita, you can add the 1/4 cup of water now and stir again. Adjust to your personal preference.
Once you're happy with the flavor balance, pour the margarita mix into an airtight container or bottle. It's now ready to be used for your favorite margarita variations!