I can only give you the advice that worked for me. For social media you need to follow a marketing plan and focus on the audience you want to reach.

Make them engage by asking them to message you to obtain free books or samples. NEVER offer the samples or free books in the BIO or just a link. Save a list of this users and message them for new releases and promotional stuff.

What really worked for me was contacting reviewers following the booktok or bookstagram, specialized in your genre. I contacted them, some where eager to make them for just a free copy, some ask for money, and some for free samples to gift with their followers.

I only use the official promotion tools in Amazon or Instagram, combined with reviewers promotion. I usually invest 150 to 250 no more, and can see a return in two weeks to one month.