One of the easiest ways to thicken your frozen margaritas is to use frozen fruit. For these Frozen Watermelon Margaritas, make sure the watermelon chunks are frozen before blending to create a thicker base. If your margarita mixture is still too runny, add more frozen fruit or some ice to the blender and re-blend. Just be cautious not to overdo it, as adding too much ice could dilute the flavor. Also, don't go overboard with blending. Blend the margarita mixture just until you achieve the desired consistency.  Finally, consider freezing your serving glasses ahead of time. Pouring your freshly blended frozen margs into frosty glasses will help keep them cooler for longer, prolonging the perfect texture long enough for you to slurp it all down!