One of the most important things to do when dropping into any level in Captain Toad: Treasure Tracker is getting a good understanding of the level's layout. You can move your camera in a full 360 degrees around the stage, which will show you many hidden rooms, gem locations, and more. When going into every level make a mental note of every room and how to enter it. Even if you can't access it straight away, you probably will be able to as the level progresses.