I'm a fan of the book Traction by Weinberg, et al. It's on the list of top books I regularly recommend to pre-seed or seed-stage companies.
The book argues there are about twenty ways to get proof points that show a business is growing. This is called "traction" and is defined as users, paying customers, press or any other measure of growth.
The authors contend that there will be one and perhaps two customer acquisition channels that work best for a startup. For example, a startup might get customers via events and billboard. For another company, awareness might be generated by search engine marketing and PR.
The key insight I like is that every business will have different ways that work for them. It's impossible to predict which ones though founders can guess and run experiments. As a bonus, this methodology works for any new business, not just start-ups.
Weinberg has a brief preview of the Traction book here on Medium.