After years of playing this game I've kind of developed a routine. Keep in mind that I live in Chicago which is the center of the country's air transport system. It's a major hub for United and American and is served by every major European carrier and some not so major. I flew Chicago-Amsterdam in January and I have tickets to go back April 7. My daughter is thinking of flying to Europe this coming summer so I've been glancing at those flights too. This first thing I can tell you for sure is that prices are up about $100 across the board from last year. I paid around $500 in January when it's normally around $400 and $600 in April when it's normally around $500.
Someone on this board posted once that, excepting last minute bargains, fares are generally at their lowest around 60 days prior to departure. Unless an unbelievable bargain pops up you're better off waitng until you're around 60 days out. In January everything was around $650 until 61 days before we left when KLM dropped their fares to $500. Shopping for the April trip, fares were $700-800. 58 days before departure KLM went to $515.
The only way to play this game successfully is to use Mobissimo or Kayak to search fares. Search three times a day. Morning, early evening and right before you go to bed, hopefully after midnight. Fare changes generally take place late at night. The thing I like about Mobissimo (
www.mobissimo.com) is that they show the price inclusive of taxes and fees. One place that seems to pick up fares that Mobissimo misses is www1800flyeurope.com . Beware though
that the fares they initially show you are before the taxes and fees are added. Once you find a fare, check out the airlines own web site. Sometimes the airline's site is a bit cheaper than the discounters and if everything is equal you're better off buying direct from the airline. If the fare should go down the airline will often issue you a voucher for the difference if you ask. If you buy form Orbitz or Expedia they won't.
The key thing is to grab the fare the minute you see it. Some of these fares dissappear almost immediately. Have a target price in mind and buy when you see a fare that's at or near it. If you're looking for a $600 fare and you see $619 buy it. Don't lose the fare for $19. When I got the ticket for April I posted a note here that KLM had cut fares. Some people tried to get the same fare a few hours later and couldn't, they vanish that quick.
Good luck