Protect the value of your boat. You may someday want to trade it in on another one.
Keep the boat clean and waxed. Having a clean hull and decks protects from deterioration from the sun and a clean hull will give you better fuel efficiency. Fiberglass should be cleaned with fresh water and a non-abrasive soap. When and if necessary, a soft bristle brush can be used to help remove stubborn debris. Cracks may occur due to stress, age or an accident. Repair or have them repaired by a professional.
If not adequately maintained metals on boats corrode quickly, especially in salt water. Keep all aluminum and stainless parts clean and polished with a good metal wax. Check all bolts, screws and fittings to keep secure.
Keep all electrical fittings dry, free of corrosion, and coat with a water repelling, non-conductive grease or corrosion inhibitor. The majority of failures in modern day boats are caused by corroded electrical systems.
Keeping your boat from the effects of the sun and rain and snow like under cover in a garage, carport or boat storage unit. At minimum keep a cover on your boat to protect the topsides, floors, seats etc.