A writer submitted a question asking about places to promote her books that are available through the Kindle Unlimited program.
Here are a few places, please feel free to reply with more:
Facebook Public Groups:
Good Kindle Unlimited Reads
Kindle Unlimited Unchained
It might be less of a problem with KU but generally I have found that you have to leave time between repeating whatever you found successful. Most say at least 90 days. A FB group for instance has a limited number of people who will down load your book. Unless it is too crowded by authors and your post quickly dissapears, you eventually 'use them up' and have to wait for more to join. Same applies to all forms of book promotion.