Another navigation aid was birds. They knew the maximum flight time of certain types of bird, and therefore if you saw that species, you would know you were within a certain radius of land.

"Islands leave distinctive cloud formations in their wake"

Only islands with high peaks, which means most likely, volcanic islands. Which happens to be true for large islands in the pacific. As opposed to purely coral islands which rise just above the sea level.

Very true. However, flat, forested islands can reflect a greenish color onto whatever clouds might be above them.

The volcanic islands tend to form pearl-chains... one making a law from the faultlines, can follow that line