Lots of indie authors who like to give advice will tell you not to respond to reviews when you get them, particularly the negative ones. I'm not one of those authors. Responding to reviews isn't just a good idea -- it's your duty.
Thank You Cards
When I was little, I had to write thank you cards for everything. Birthday, Christmas, Easter baskets -- I was told to say thanks for it all. I hated it, and swore I would never deal with that nonsense again once I became adult.
And now, I'm going to tell you to do the same thing I hated to do when I was a kid. I want you to write your reviewers, and say thank you. Because you do have to respond, even to the really ugly reviews, and the response is always the same: thank you.