Ensure your content is structured in a way that users understand.
Ask users to organize content into groups that make sense to them.
Test if your content's description matches your user's description.
Card sorting helps you understand what makes sense to your users.
Card sorting studies can be run in one of two ways: open or closed.
In an open card sort, users name the categories they have organized the content into.
In a closed card sort, users are given pre-defined categories and asked to organize content into these groups.
Card sorting can be conducted early in the design process before wireframes or prototypes have been created.
For digital card sorts, you need to decide whether to run open or closed card sorting, and whether to go moderated or unmoderated.
You'll need to define the topics you want sorted, and these should represent the main content on your site or app.
Learn how to present your online content and labels for optimal findability.
Quick answer: as big as possible. With an addendum: so long as it’s organised correctly