Your Engine
Make sure your motor is tuned and in good running order. For carbureted outboards, install new plugs, look for oil leaks, check fuel lines and filters, change the lower-unit gear oil if you didn't do it before winterizing, and check all fluid levels. Four-stroke outboards may require additional steps, so review your owners manual or seek qualified service. For inboards, again, check all fluid levels, look for any sign of winter damage. Clean the motor of oil and grease, check fuel filter, gas and oil lines, vent hoses and make sure the gas tank has fresh gas in it. Start the motor to ensure that it operates properly and shifts correctly. Check your steering linkages, too, to make sure they operate freely, aren't rusty and that all anchor points are secure.

If you flushed your cooling system with antifreeze, flush it again BEFORE getting to the water. Certain types of antifreeze are toxic to fish and wildlife.

Your Boat
Check your boat for dry rot, cracks or leaks. In a wooden boat, poke at joints with a screwdriver to make sure the wood is firm and not deteriorating. Many fiberglass boats have plywood within the transom - look carefully to make sure the plywood is still rigid and not deteriorating. Make sure the bilge pump is functioning or that you have a bailing bucket on board.

Your Trailer
Check your trailer for rust - it can weaken ball hitches, weld points and springs. Damaged areas should be repaired. Sand off and prime any rust spots you find to prevent further damage.

Check tire inflation and brakes and brake fluid. Spin the tires to ensure that bearings are operating freely. Make sure bearings are well-lubricated.

Lubricate all rollers, pivot points, the winch, and the coupler.

Look for signs of cracking or metal fatigue. Tighten bolts and screws and inspect the electrical system for worn wires or loose connections. Lights are vulnerable to corrosion, so pull off the covers and make sure bulb is not corroded to base. The bulb bases inside taillights can be sprayed with a light oil to keep moisture out.

Safety Check
Check to make sure all the required equipment is aboard your boat. Carry appropriately sized life vests for each user and make sure they aren't waterlogged, torn or deteriorating. You'll need an approved throwable flotation device, too, a sound-making device such as a whistle or horn, and, if operating in coastal estuaries, a visual distress signal. Depending on your boat, you may need a fire extinguisher and other equipment - check regulations. Lack of any of these items is a citable offense.

Any boat operating before sunrise or after sunset must display navigation lights. Many sporting goods stores or boat equipment stores carry clip-on lights.