Business rules, like all requirements, will inevitably be changed and re-prioritized, so they should be organized and managed in ways that make these adjustments as easy as possible. One of the most efficient ways to manage business rules is by storing them in an updatable tool such a business rules repository. It's easier to use, maintain, and validate the business rules from within the repository, separate from other business requirements. Exactly how you organize your business rules will depend on your project and environment, but here are some possibilities.
Organizing by value. Because the business rules exist to support a business goal, you can organize the business rules by the business goals they support. This is a proven strategy for prioritizing and organizing the business rules. The more valuable the business goal, the more valuable the corresponding business rule. The greater the degree to which the business rule supports the business goal, the higher the priority of the business rule.
Organizing by concept. You can also organize business rules by concept. For example, you can group all of the business rules about customers, orders, etc. Organizing the rules by concept will remind you to state the rules with their associated concepts. Organizing by concept is also useful when testing or validating the business rules.
Organizing by function or feature. Whether you use an automated or manual business rules management system, it will give you the flexibility to organize the rules by grouping them according to their corresponding function, feature, use case, etc. Thus, you could group the business rules that apply to a use case so that you can report on and validate the rules together. Caution: while it may be useful to review (or report on) the rules this way, you wouldn't want to store the rules with this type of organizational structure, because a business rule may apply to more than one use case or function.