Note: if you don't have a good, high-speed blender, you may find that the skins from the blueberries don't get blended as smoothly as you would like. If the texture is a little rough, you can add ice to thicken it up, which will make any bits less noticeable, or you can pass the smoothie through a sieve to remove any pieces the blender couldn't manage.
You can use fresh berries instead of frozen, but in this case I recommend opting for a handful of ice to thicken the smoothie and cool it down.