I suggest making a single serving first and taste it so you can add more/less tequila, mezcal or syrup to your liking. Everyone is different and prefers their drinks a different way, so feel free to add more or less tequila, more simple syrup, more lime juice, etc. This is my absolute favorite combo listed above.
Before serving, rim the edge of the glass with a lime slice and then dip it in coarse salt. Fill the glass with just a few ice cubes or even with crushed ice – my ice preference of late.
In a shaker with ice, combine the tequila, mezcal, grand marnier, strawberry juice, lime juice and simple syrup. Shake well for 30 seconds, then pour it over the crushed ice. Add a lime slice and a strawberry and serve!
As a note, I like to char the strawberries for garnish too! I do this on the grill or on the gas stovetop burner.
For simple syrup, I bring equal parts water and sugar (so, like 1/2 cup each) to a simmer in a saucepan while whisking. Let cool completely then store in the fridge!