1). Check Your Tires
The tread on a tire works to create grip on the road by filtering water, mud, and debris away from the contact patch. After awhile, the tread wears down and becomes much more likely to slip or spin on wet surfaces.
If anything else, Use the penny test to check. Get a penny and insert it in the tread with Lincoln's head pointed at the center of the wheel. If you can't see his hair, your tires are good. If you can see the top of his head, it's time for new tires.
2). Make sure your Windshield Wipers are solid and don't leave behind streaks or patches
3). Turn ON Your Headlights(Duh)!
It's amazing how many people don't do this-Part of the problem is Most cars' lights are already set to automatic for the most part, but sometimes the button or switched gets moved and people forget. It can be a very dangerous move and costly mistake to forget this simple task.
4). Avoid HydroPlaning
Ok, here's the REAL scoop with Hydroplaning-
If you're moving fast enough, your tires will skim over the surface of the water, causing you to hydroplane & possibly lose control of your vehicle.
If you start to hydroplane, keep both hands on the steering wheel and slowly apply the brakes. Slamming on the brakes or jerking the wheel can cause you to skid. The best way to avoid this situation altogether is to look far down the road and reduce speed when you approach a puddle.
5). Never, EVER use Cruise Control
Cruise control is helpful when roads are dry, but can be a problem when it's raining. Cruise control works to maintain a constant speed, so it greatly increases the chances of hydroplaning since it's not smart enough to detect when there's water on the road. Keep your car under full manual control any time you drive in the rain. Unless you own a Tesla, and even then I would suggest being in control of THAT car, don't "Use the Cruise".
6). SLOW DOWN
Wet roads can be slick and treacherous, increasing stopping distances and the potential for a skid. Give yourself more time to react by driving 5 to 10mph below the speed limit. Keep right, pass safely, always check your mirrors, and leave several car lengths between you and the driver ahead. It might seem like common sense, but anything you can do to be a slower, more attentive, more courteous driver makes rainy weather safer for all drivers.