If you have been procrastinating on booking your holiday air travel plans, do it now! That's the advice of several travel search and booking websites, which track airline prices year over year to predict how they will change on key dates.

For the American Thanksgiving travel week, the advice is—well, that you should have done it weeks ago. But if you've put off the task, the sooner you do it, the better. Hotwire advises travelers to avoid flights on the Wednesday before Thanksgiving (Nov. 27 this year) and the Sunday after (Dec. 1) because those are typically the most expensive times to travel. Fly out early on Thanksgiving Day (Nov. 28) and return the Saturday after the holiday (Nov. 30), and you'll likely see the best prices.

Another way to shave a little money off Thanksgiving air travel is to get your checked bag fees reimbursed, a deal that Orbitz is offering to anyone who has booked their flights via the site. Travelers who booked via Orbitz flying anytime on or before Nov. 30 can use the Orbitz mobile app to "Zap that Bag Fee" and earn $25 toward their next hotel booking.

For late December travel in the U.S., the time is also now or never to book flights, although Christmas bookings are a little more forgiving than those for Turkey Day if you book as soon as possible. Search and booking website Hipmunk recently crunched some numbers to find that historically, you're in the clear to book airfare for Christmas as long as you do so before Veteran's Day (Nov. 11). Prior to Veteran's Day, travelers saved an average of $266 compared with those who booked later.

Information from Kayak.com suggests travelers will get better fares around Christmas if they travel as close to Dec. 25 as possible. Last year, people who did so saved about 20 percent on average. You might also get better fares by avoiding weekend travel dates near Christmas, when Kayak sees prices rise 24 percent in the U.S.

Hotwire says the day before Christmas is historically one of the more expensive days of the year to travel. But with the holiday falling mid-week this year, it could lessen demand for travel over the weekend. Hotwire suggested keeping your options open, and checking out flights over the weekend before Christmas, as well as the Friday (Dec. 20) and Monday (Dec. 30) that border it.

Another way to get a better fare, according to Hotwire, is to include lesser-used airports, like those serviced by JetBlue and Southwest, when searching for flights.

Should you need a hotel during the holidays, you might actually be better off waiting than booking early. Because many travelers stay with family over Christmas, and leisure and business travel during these times is down, several cities are showing drops in hotel rates. Hotwire says you may see very steep discounts if you wait until the last minute or even the day of to book a hotel for Christmas.

Orbitz is showing Christmastime hotel prices in three of its top 10 travel locations to be much lower than last year: Denver (down 22 percent since last year), Phoenix (down 15 percent), and Las Vegas (down 8 percent).

Next year, try to nab those flights between September and mid-October. Kayak says that after mid-October, airfares for Thanksgiving increased up to 17 percent, 51 percent for Christmas, and 25 percent for New Year's Eve.

For more travel information, see 15 Best Travel Apps, The Best Travel Sites, Top 5 Travel Search and Booking Apps for iPhone, and Top 5 Travel Guide Apps for iPhone.