The rules have changed. Here’s what you need to know.

Fares, advance booking requirements, and valid dates of travel now vary significantly from one airline to the next. Here are 10 things you must know to get the best deal.

Los Angeles, long a high-fare airport, could experience a fare revolution when All-Business Class carrier MAXjet starts service Aug. 30. LA-London starts at $1,398 round-trip. The airline already offers low fares to London from Las Vegas, New York, and Washington, DC.

Continental leads the low-fare charge for summer travel to Europe and flies to 21 European cities. Downside: You must book 60 days in advance and most fares are only available from its hubs in Cleveland, Houston, and New York/Newark. Upside: Business Class fares start at $1,448 round-trip. Travel completion deadline, Sept. 6.

American is matching Continental on some routes. (Delta and United are not.)

If there isn’t a low fare from your departure city, try buying a separate ticket to a gateway offering a low fare.

Check alliance partners. If your preferred carrier is Delta, which is not discounting as heavily to Europe at the moment, check its SkyTeam partner Continental, which might have a $1,498 fare—and still net you Delta miles and elite status credit.

First Class: 2-for-1s are available from British Airways via its Visa Card (877-376-3135) and SWISS via Amex’s International Airline Program.

Premium Economy: Best seat is on Virgin Atlantic, starting at $1,236.

Eos is running a special weekend fare of $1,750 round-trip, more than $1,000 less than its usual fare. (Ticket by June 15.)

Short-notice: Star Alliance member US Airways has quietly launched new Business Class fares in many markets, with no advance purchase, starting at only $1,998.

Northwest is offering fares starting at $1,598 from New York to a number of cities in Europe, with travel valid through the end of September. Downside: 50-day advance purchase.

Domestic First Class Awards Slashed

American Airlines and Citibank are so proud to celebrate the 20th anniversary of their co-branded credit card, that they are discounting domestic mileage awards to shockingly low levels. You can now redeem 20% fewer miles for travel on select “MileSAAver” awards to Hawaii, the Caribbean or Mexico, and to cities in Canada and the US.

Domestic (49 US and Canada) First Class awards start at only 36,000 miles (award code CA2036U), and only 48,000 miles on three-class transcon flights (CA2048U). Caribbean First Class awards drop to 48,000 miles (CA2048C), and Hawaii First Class starts at 60,000 (CA2060H).

Reservations must be booked and ticketed by June 30, 2007 for travel between Aug. 22 and Nov. 16, 2007. Discount only available for Citi / AAdvantage US domestic and Puerto Rico credit card members. No registration required. Details: (800) 882-8880.