How to identify which assumptions to test first

Use this when

You have a business direction in mind, but you are not sure what to validate first.

Open your startup workspace and review your current Lean Canvas.
Start with the assumptions behind your Customer Segments and Customer Problems, because these shape everything that follows.
Open Builder and work through Refine Customer Segments and Customer Problems until both are clear enough to test.
Check whether your Customer Segments describe the right groups of customers – people similar enough that the same solution, message, and channels could work for them.
Check whether your Customer Problems describe obstacles that seem important enough to explore further.
Prioritize the assumptions that matter most if they turn out to be wrong – especially whether you are focusing on the right customer segment and whether the problem space is worth validating.
Start Problem Validation Research for the selected Customer Segment. IVA will use your current direction to identify the relevant Job-to-be-Done – the job the customer is trying to get done – and explore the frictions customers face while trying to do it.
Use the research results to see whether the actual Customer Problems match your assumptions, and refine your direction from there.

A clearer validation focus, so your first research round tests the assumptions that matter most.