One approach is to identify and analyze the most and least important in the delivery product. Consider rational inclusion/exclusion criteria based on the product such as;
Building a broad testing coverage
Identify major features users will actively interact with
Identify the most complex and potentially problematic components in the system
Consider prioritizing several test cases that have higher business value and are cheaper to execute as opposed to one big expensive test
Test cases which cover new features bring more incremental use than those covering partly old and partly new features, it is ideal to incorporate both
