This is another of my favourites for tweeting about Independent authors and their books, and they really helped me out with lots of shoutouts when I was started out (for which, I am very grateful).
IARTG has a substantial following (74.8k at the time of writing) and how it works is that you follow @IARTG. Once you have done so, you can then use the hashtag as well as sharing tweets of interest to you that are using it. I’ve found a few great books to read via IARTG.
As you can see from the hashtagify embedded below, IARTG works well with a lot of other great hashtags and a combination of these will (hopefully) see your tweet spreading far and wide.