I've written about this in detail on my blog here, so I'll summarize my thoughts below! Messaging and positioning work is never complete, so always treat your positioning doc as a living document that will evolve with your business.
The framework I like to use involves starting with jobs to be done:
Step 1: Start with the ‘jobs to be done’
What: Define the ‘jobs’ your product can be ‘hired’ to perform
Why: As Peter Drucker once said, customers don’t buy products or features, they buy benefits. Jobs-to-be-done helps you look at your product from your customers perspective, making it easier to separate the benefits from the features.
Step 2 Segment your TAM
What: Segment customers in your TAM using obvious and visible characteristics.
Why: For segmentation to be effective, it needs to be based on obvious and visible characteristics to accurately validate your messaging.
Step 3 Map jobs to be done to benefits
What: Map the ‘jobs’ each segment cares about to the benefits delivered by your product or feature.
Why: Each customer segment does not care about all the benefits you have to offer. Mapping helps you identify which products or features, and therefore benefits you highlight when positioning your product to a particular customer segment.
Step 4 Analyze competitive alternatives
What: Analyze alternatives available to each customer segment for these jobs
Why: You can’t identify and articulate benefits in a vacuum.
Step 5 Articulate your value
What: Articulate the value your product provides relative to the alternatives in a way most likely to resonate with each segment.
Why: This is where you bring your positioning home. Having identified the jobs to be done, benefits, customer segments and competitive alternatives, it’s much easier to articulate the value of your offering.