SpaceX's innovation was looking at the market and deciding that Iridium was right but about two decades too early. A lot of people in the industry (and a number of governments as well) lost big when Iridium went bankrupt, and quite understandably the large players were content to stay in their lane. After all, ULA came about basically because the DoD needed two technologically diverse launch platforms, but wasn't willing to commit to the launch cadence needed to keep both commercially viable under separate parent companies. If there hadn't been a future with customers ready to fly, and launching enough to survive a couple launch failures, SpaceX just would have been the upstart with high insurance costs.
Hardware-wise, SpaceX did a great job gathering the best of what had already been done and proven. Friction stir welding? Used to build Delta II, Delta IV, Atlas V, Space Shuttle tank and more. Pintle injectors? Lunar Excursion Module. Semi-balloon tanks? Proven on Atlas I and II, and Centaur. Then, once they had something that flew, and a contract from NASA to keep it flying, they iterated on it to make it reusable. Much like the story of Boeing with the KC-135 and 707, a key early contract was enough to support the program and subsidize further development.
Hardware-wise, SpaceX did a great job gathering the best of what had already been done and proven. Friction stir welding? Used to build Delta II, Delta IV, Atlas V, Space Shuttle tank and more. Pintle injectors? Lunar Excursion Module. Semi-balloon tanks? Proven on Atlas I and II, and Centaur. Then, once they had something that flew, and a contract from NASA to keep it flying, they iterated on it to make it reusable. Much like the story of Boeing with the KC-135 and 707, a key early contract was enough to support the program and subsidize further development.