With a long history of involvement in NASA flagship astrophysics missions, Ball Aerospace has made key contributions to Hubble, the new James Webb Space Telescope, and the upcoming Nancy Grace Roman Space Telescope. Here, we share lessons on both technical and programmatic topics gleaned from decades of productive experience in constructing system performance budgets, accelerating the initial design process, defining the philosophical approach to requirements, planning for serviceability, leveraging design complexity, accounting for subsystem interactions, breaking down barriers to cross-team collaboration, building a team capable of meeting long-term goals, integrating the customer into the enterprise, and promoting a team mindset that enables high achievement in the face of immense challenges. The teams designing and building the future Habitable Worlds Observatory can apply this knowledge to complete the next flagship mission more quickly and effectively with less expense.