Tips from my experience

* Whatever you do, try to talk to customers (not friends) as early as possible, and try to keep them in the loop when taking critical decisions. Frequent feedback can keep you on the right direction and also not lose morale. (Nothing like a long release cycle to invite self doubt and other self destructing emotions.) - Try to find the venues (online or offline) where people who can be potential customers hang out and interact.

Apart from other recommendations below: (Blue Ocean Strategy, Expanded Edition: How to Create Uncontested Market Space and Make the Competition Irrelevant )[https://www.amazon.com/Blue-Ocean-Strategy-Expanded-Uncontes...]

Different [1] is one of my favorite books on how to find a unique niche in crowded markets. It is written by a (brilliant) marketing professor but is useful for product strategy. Also see Blue Ocean Strategy [2] on this topic.

Essential had neither of these approaches.

[1] https://www.amazon.com/Different-Escaping-Competitive-Youngm... [2] https://www.amazon.com/Blue-Ocean-Strategy-Expanded-Uncontes...