Venice is saturated with lodging options, but it is also one of the most popular destinations on earth—so book your lodging as far in advance as possible. Planning your trip four to five months (or even farther) ahead will give you a much greater selection. Double-booking is not uncommon, unfortunately, so make sure you take your reservation confirmation along with you, including any special requests you've made (tub or shower, first or top floor, and so on). Almost all hotels can be booked online, either via email or using the booking system on the individual hotel's website—where they often guarantee the lowest rates and even discounts for longer stays or last-minute requests. You can also try larger booking portals such as venere.com or veniceby.com.
Venezia Sì (041/5222264 Daily 9 am–11 pm www.veneziasi.it firstname.lastname@example.org), the public relations arm of AVA (Venetian Hoteliers Association), also offers online booking for almost all hotels in town, and you can make reservations through them by phone or email. If you're in Venice without a room booked, try making same-day reservations at one of the AVA booths, which are at Piazzale Roma (Daily 9 am–10 pm), Santa Lucia train station (Daily 8 am–9 pm), and Marco Polo Airport (Daily 9 am–10 pm).
They also have counters at the San Marco and A.S.M. Parking Garages in Piazzale Roma.