To travel between the islands, you'll want to craft a bucket early. Before that, you can use boats to avoid fall damage.
An example of the layered generation of floating islands. Lower islands tend to be more dangerous, being shrouded in darkness by islands above them.
Due to the lower islands not being covered in dirt, you can find valuable resources easier in the lower levels of the world. Since light rarely falls down to the lowest layers, mobs spawn more frequently.
Due to the way ice spikes generate, you'll find enormous ice chains linking the islands in the ice spikes biome.
While ores are rarer at the surface, searching the lower sides of an island from another island below is a solid mining strategy. Especially deserts are interesting, since diamonds spawn more frequently there.