First I would try to figure out where is the location of the island.If it's near the land,I may try to swim back to land.If it's near path of ships,I may try to prepare things to make signals.If it's in the middle of nowhere,I would find fresh water sources first,then try to find sources of food or tools that can help me get foods.I would dig a hole and hide myself from sunlight,and the hole may collect rain water.And I will start to pray to the God.