Served in an ice filled glass. Garnished with a long spiral of citrus peel.
Perhaps the hardest part about a Cooler is its garnish. It is also what differentiates it from what might otherwise be called a highball. The garnish is a long continuous spiral of a whole lemon, lime, and/or orange peel, which is placed into a Collins glass before adding the ice, a spirit, and then topping it off with soda water.
For an example, see: