Driving in the rain requires your complete attention, so anything that will distract you must be turned off. Also, studies have shown that the most important thing to do to remain safe driving in the rain include slowing down to avoid hydroplaning. Plus, leaving your headlights on low-beam at all times, so your vehicle is more visible and allowing more space between your vehicle and the one in front of you. This information was compiled in part from the American Automobile Association and the National Safety Council. Finally, make sure your tires are in good shape and properly inflated.
For more info, see What are the Safest Cars to Drive Depending on Terrain