The following guidance focuses on big-picture strategy.
4 Pillars of Book Marketing, or How to Sell More Books in Less Time by Matt Holmes
I write in Publishers Weekly about
setting goals and assessing your resources
before you get overly into the tactics.
Find your marketing sweet spot by Ricardo Fayet:
https://www.janefriedman.com/the-importance-of-finding-your-marketing-sweet-spot/
Barbara Linn Probst offers advice on a three-tiered approach to book launches:
marathons, sprints, and pounces
How to develop a marketing and promotion plan as an indie author, by Emma Lombard:
https://www.janefriedman.com/marketing-and-promotion-plan-indie-author/
Niche versus general book marketing, a Business Clinic session:
https://youtu.be/NtHp7yJebB8?si=ikn3ZdgQYuBM3Vvl
How some self-published books thrive without viral marketing
(or other tricks)