I'll probably write a blog post at some point covering the things I've tried, which is admittedly not a lot. There are vanishingly few free marketing channels, and paid marketing typically only makes financial sense once you've got at least a few books to increase your revenue per reader. Otherwise your customer acquisition costs exceed your margins.

If you're writing fiction, the best freebie I've found is sending advance review copies through Voracious Readers Only. They limit you to twenty without paying, but that at least got me a pair of reviews on Goodreads (sadly nothing on Amazon).

If you have specific questions, I'll answer them to the best of my ability. Whether you want to take advice from the guy who only sold ten copies is up to you.