[Q] Any Tips on Promoting Erotic Kindle Books?

A friend of mine wrote a 5 erotic kindle books. I want to help him to promote his book. What are the best places to promote them?
Especially the free one. I know about Reddit and Facebook groups.

You can promote on popular adult sites, the erotica ones....then add a link to the kindle books on your profile. You can try literotica and lush, just google it.

If the content is good, people will buy.