This goes to the very core of what it means to work for a private equity firm. You should be able to walk into an interview with four to five solid examples of how your actions directly saved your previous employers money. This could be from developing operational efficiencies to ferreting out information that helped save money on a M&A deal. Maybe your research helped a company develop a new product line, or your ideas spurred cost savings on benefits. Whatever it is, be prepared to talk frankly and in detail about how you are an agent of value creation.