When I began publishing, back in the 1980s, there wasn't much required from authors to make their books successful--other than the writing itself.
Sounds dreamy these days, doesn't it.
On my first books, the publisher assigned a publicist who set up gigs and I just showed up (talks, panels, interviews). Any paid advertising happened behind the scenes and brought sales. One of my early books even won an award, and I only found out after the fact.