The best way to apply for jobs on cruise ships is to go to the web sites of the different cruise lines and seek out the sections where it mentions employment.
There are also a few web sites that list open jobs on cruise ships. I just did a Google on "Cruise Ship Open Positions"
and I found many sites.
teaching art, however is NOT a high-demand skill on cruise ships, unfortunately, and it is one of those skills that a lot of people possess. Cruise Lines are inundated with offers from people to do this in exchange for free cruises, and some of them take them up on it. It's a one in a million chance however, I can only think of two ships where I know they have dedicated art teachers, and I don't think they pay.