Heads: As any boat owner knows, all heads are not created equal. Even similar brands have their own idiosyncrasies. Follow the crew's instructions on how to use them correctly. If in doubt, ask before use.
Water and showers: Charter yachts carry plenty of fresh water for both cooking and daily showers, plus rinse-offs on the stern after swimming, but use water conservatively. Your crew will explain specifics.
Lights: Locations of lights and switches, if not obvious, will be pointed out to you. Most charter yachts have significant battery banks. Nonetheless, whether plugged into shore power or operating from the ship's batteries, follow the standard rule: Use them as you need them, but always turn off lights when not in use.
Electrical outlets: Be aware that locations and dedicated use vary from boat to boat. Certain outlets (such as inverter outlets) might have use restrictions, such as for charging phones or laptops only. Some might not work unless a switch is turned on. Others might work only if the boat is hooked up to shore power or when the generator is running. Your crew will explain which outlets can be used for what, and when. Heed your crew's directions. If you're unsure, ask before plugging in.
If you're chartering with kids, remember that professional crews are not babysitters—they have many other daily jobs to do—so don't expect them to do so. (This is spelled out in many crewed-charter contracts.) Most crews, however, are kid-friendly and might offer to entertain your children for a certain amount of time during the charter. If they offer, you can graciously accept, but don't abuse the privilege or expect them to do it full time.
When in harbors, be courteous of crews on neighboring boats when socializing in the cockpit early in the morning or late at night. Keep noise to a minimum before 8 a.m. and after 11 p.m. Music and lively conversation carry loudly and easily over the water.
Keep community living space tidy. Your crew will do the bulk of the cleanup, but you can help by keeping personal items such as clothing, towels, hats, sunglasses and toiletries (including sunscreen) out of the main saloon. Stow them in your cabin or in a designated area on deck.
Crewed yachts with cooks usually have special areas, sometimes even a dedicated fridge, where help-yourself-anytime snacks and drinks are kept. Your cook will point these out to you. Before you help yourself to anything in the main galley fridge or lockers, be sure to first ask the cook—he or she likely has plans for it. During meal prep, some cooks welcome help in the galley if guests are so inclined; others do not. If you ask and are politely refused, respect the cook's wishes. Kick back, relax and stay out of the galley.
Remember that, as on all boats, the captain's word is law. If weather conditions or other safety or time constraints prevent sailing to a given area, don't argue the point. The captain and crew want to provide you the best vacation possible and, within reason, cater to your every wish—but they are also ultimately responsible for your safety and the safety of the boat.
During the charter, many brokers suggest that guests treat the captain and crew to dinner ashore on one night. This is entirely optional, but your crew will appreciate the gesture.
At the conclusion of the charter, it's customary for guests to leave the crew a gratuity of between 5 and 15 percent of the charter fee, based on the level of satisfaction with the crew and the trip. Good crews will never let you see how hard they're working to take care of your every need, but they work very hard, usually from early morning to late in the evening, so keep that in mind when determining how much to tip.