Before jumping into that raft, it's important to know how to swim. Even if you're a strong swimmer, always wear a life jacket. It should fit snugly and have back and shoulder protection as well as floatation to help you swim safely in white water. Also, don't forget to wear your helmet—it should be designed for water sports, fit properly and snugly on your head, and allow for water to drain from the helmet. It should also cover your ears, temples, and the back of your neck. Once you have the proper gear and are sure it's all in working order, you're ready to run the river.
It's also really helpful if you've done a little exploring first. Make sure you know the river you are rafting on—check out the rating of the rapids and what the current is like. It's best to a have a trained, experienced guide on your team and in your raft. The guide will know the best course and the safest passage. Don't enter a rapid unless you're sure you can run it safely or swim it without getting hurt. If you fall out of the raft, position your body so that you are on your back with your feet facing down river—try to keep your feet and legs up.
Usually a group of three boats is the minimum on a river—but only one boat should run the rapids at a time. Safe rafting is all about teamwork, so pick a captain to call out directions so everyone can work together.
Most importantly, be prepared! Get a first aid and survival kit, and include extra ropes, a raft repair kit, and extra life vests. Better safe than stranded!