This is not one of those prompts in which you are asked to contemplate how one man is an island unto himself. Or how loneliness feels like being stranded on an island.
Unless, of course, that is what you choose to write about!
Instead I want you to think about an island you have visited. Close your eyes and picture what it looked like. The shape, size, construction of the beach. Were the shores sandy or rocky or a little of both? Were there smooth descents to the sea or sharp cliffs?
Did the waves lap like in a bathtub or crash like thunder?
Were people swimming or surfing or playing catch with dogs? Or only sitting serenely on the beach and watching?
Who was there with you? Family or friends or both? Where did you stay? If in a beach house, what did it look like? How far from the beach was it? What could you see from the windows?
If in a motel, ask yourself the same questions.
What was the town like? Was it tiny with only a few touristy shops or a huge metropolitan setting?
Make lists. Endless lists of things you saw, smelled, touched, tasted.
Think of at least one character that could populate your scene. It would be best to have two, but no more than three.
Think of the story you will tell. Will it be a romance or a horror story? Will your character meet the love of his life or be killed by a demented person?
Once you have setting and story in mind, write. Put your character in the scene and make things happen, one event after another. Keep the momentum rolling so that there is an even pace.
When you are finished, reread and edit.
Have fun with this one!