Marketing: how much effort does this technique take; how durable is the effect of the technique; what is the impact of the technique? Three axes for a graph: effort, durability, impact.
A book review is high effort, high durability, high impact. A single tweet is low effort, low durability, low impact. A well-coordinated social media campaign is high effort, low durability, high impact (although it could be made much more efficient over time).
A good cover is high effort, high durability, high impact.
Writing in a series is high effort, high durability, high impact.
Writing to market trends is high effort, low durability, variable impact (it’ll depend on how well you write). Writing to your own personal drummer is high effort, high durability, low impact (but that may change over time, as people find the books they love without the boost of having alsoboughts behind them).
The high effort techniques can probably be made more efficient over time; you can search around for a minimum effort/maximum impact solution and go for medium effort for medium impact with medium durability (writing a pulp series in a popular category that you love already, setting up catchy covers/blurbs/advertising materials for a repeatable social media campaign, etc.).
The ideal would be low effort, high durability, high impact. Have I come up with anything that fits those criteria, even a hypothetical example? Nope. Even the ideal BookBub ad would be low effort, low durability, and high impact.
But now I know that if I ever see such a unicorn, I should get on and ride.