Always wear a life jacket, and be sure there is one for each passenger on board. Wearing a life jacket can prevent a person from becoming completely submerged if falling into the cold water, and help prevent involuntarily inhaling water from the natural gasp reflex, which can cause drowning. A life jacket can keep you afloat and dramatically increase your chances of survival.
Dress appropriately for the water temperatures and not the air temperatures when going out onto the water.
Whether powerboat, sail or paddlecraft, make your on-water activities social. Share where you're going and when you'll be back with family and friends; file a floatplan.
Use the buddy system and never go out on the water alone.
Wear reflective clothing to make it easier for searchers to spot you if you fall overboard.
Carry and register a Personal Locator Beacon in addition to a VHF-FM marine radio to immediately alert the Coast Guard and local response agencies of potential distress.