Look at your audience and the type of tasks they undertake when interacting with your product. These task based audience segments are basically groups of people who do similar things.
grouping audiences by differences in behaviour is important
You then gather actual users and have a conversation with them, collecting their perspective. This is usually in the form of an interview or one on one research.
analyze all of these conversations and composite them into a mental model diagram. Compare all of the things your solution is supposed to do with the different parts of the mental model diagram