Take about a cup of fresh or frozen blueberries (preferably wild, which are more flavorful), and puree or mash them to release their blueberriliciousness. Put about a tablespoon of sugar in there while you're at it to get it blended in. Strain through a fine strainer into the glass, and add a some lemon juice, from a splash to a tablespoon, depending on the berries. Add a shot of vodka and mix. Or I guess you could be putting this all in a shaker to shake it, but then it might be kind of frothy at the end. Some water may be in order to prevent it from completely blowing your mind.

The blueberries really aren't garnish, do not listen to extratasty and its fascist ingredient-sorting.