You should always reserve a room for at least the first two or three nights. When entering the U.S., you must complete the I-94 form (Arrival-Departure Record). One of the questions on the form is the address where you will first stay. Another reason to book the first nights of your stay is that upon arrival you will most probably experience jet lag, or you may want to check into a reserved hotel room so you can rest and look for hotels for upcoming days in a leisurely manner. Please be aware that during high season, holiday weekends or during the convention season, hotels in certain cities may be fully booked. During the cooler months, the farther south you go, the warmer it will be. Fort Lauderdale, Miami, the Keys, Marco Island and Naples will have the warmest water during the winter.