Send me an e-mail and I'll send you curated resources that were useful over the years. I can't write a thorough reply right now and there are many layers to it.
TL;DR:
A market you can reach that can buy a product you can get distributed.
It's advantageous if you enjoy interacting with the people you want to solve problems for, especially initially (many calls, emails, conversations).
The product's sale complexity (high-touch vs. low-touch or self-service, buyer-is-user vs. buyer-is-not-user but can make discretionary decisions vs. purchase signed off by a committee) will impact what you do. Continually reduce the sale complexity.