This is a post in itself. But I guess the main thing here is to take time for crafting a value prop before the time you urgently need it. Even if it's not perfect, start using it. When it works, great. If not, have another stan.

How to do it? Talking to lots of customers helped. Having founders keep talking about product vision until it started making sense to yours truly helped - there was development both on their and my part. Being in the business for more than 1-2 years helped as I developed a better sense of what customers wanted and what competitors were/are doing. Also, basic market research helped.