Mike Hartington, the Director of Developer Relations, addresses common concerns about app performance, specifically focusing on identifying and resolving startup and runtime issues. He suggests using tools like Lighthouse and Webpage Test to measure startup performance metrics such as resource download time, time to show content, and time to interactivity. For runtime performance, which involves analyzing code execution time, layout complexities, and animations, Hartington advises deferring data fetch requests using lifecycle events to prevent performance bottlenecks during page navigation. He also highlights the importance of sharing data across components to minimize unnecessary network requests, thus improving app responsiveness. Using the example of his Star Track app, Hartington demonstrates practical solutions to enhance performance and invites readers to share their own experiences with performance challenges.