For a spicy rim, run a lime wedge around the outside of the glass, then dip the glass in the tajin coating the entire rim in the seasoning.
Add the fresh jalapeño slices, lime juice, agave syrup, and orange juice to the bottom of the glass. Then, using either a muddler or the handle of a wooden spoon, muddle the jalapeño to release some of its flavor.
Fill the glass with ice, then top off the margarita with the club soda or sparkling water. Cheers!