Obviously Awesome by April Dunford is a solid marketing book subtitled How to Nail Product Positioning So Customers Get It, Buy It, Love It.
Dunford covers how positioning is the act of deliberately defining how you are the best at something that a defined market cares a lot about. Customers need to be able to easily understand what your product is, why it's unique, and why that matters to them. She goes on to note that positioning can be thought of as context-setting. Most products are exceptional only when understood within their best frame of reference. Great positioning takes into account the customer's point of view on the problem you solve, alternative ways of solving that problem, and how you're different than them.
Additionally, Dunford writes how the worst part of standard "who is it for, what does it provide" positioning statements is they assume the marketers know the answers. Rather, the most enthusiastic customers are the best people to say what a given product is, why it's unique, and why that matters to them. Marketers should try to find out what these fans of your product would do if your solution didn't exist, what's their alternative? Understanding what your best customers see as true alternatives to your solution will lead you to your differentiators or unique attributes. Also, the characteristics of these most enthusiastic customers are important as determining who they are means others with these same characteristics can be targeted.
There's interesting concepts in the book and Dunford closes with steps on how to go about positioning, and then how to write it up as part of a positioning canvas:
Step ten - capture your positioning so it can be shared.
3. competitive alternatives - if your product didn't exist.
5. value that those attributes enables for customers.