Several good answers.
Additionally, they knew the paths of certain stars, where they rose and which ones would pass directly overhead. By navigating from one location where they knew the star patterns they knew they could always return. They did not have the North Star, being in the southern hemisphere, but once they found Hawaii they could use that one. This implies they sailed and navigated at night and rested during the daylight hours.
Also, by watching for signs like clouds that always were in the same place, birds that nest on land and flew in specific directions at dawn and dusk, small changes in currents that flowed around an island, debris in the water, a greenish tinge to the underside of clouds, etc., they could determine that land was in a specific direction.
The novel, Hawaii, by James Michener talks about this. Granted, the book is fiction but he was known to research and to get his facts right.