How do I get better at complex approaches when navigating a flight?

You can navigate a normal flight well, and now it is the complex approaches, the busy, tight, high-workload ones, that trip you up. That is exactly where the difficulty should be. Those approaches pack more decisions into less time than anything else you do, and struggling there means you have reached the demanding edge of the skill, not the limit of it. What makes a hard approach manageable is not reacting faster, it is being further ahead. The pilots who fly them smoothly are not quicker in the moment, they have already thought through what is coming so the workload does not pile up all at once. When you are behind the aircraft, everything feels frantic. When you are ahead of it, the same approach feels ordered. The whole game is staying ahead. So brief the hard ones cold, on the ground, before you ever fly them. Walk through the approach step by step, name where the workload spikes, and decide in advance what you will do there and what would make you go around. Practice them in the sim until the sequence is familiar. The complexity does not shrink. Your readiness for it grows until you are meeting it prepared instead of surprised.