If anyone can figure out how airlines come up with the pricing and routing they come up with, they should be nominated for some sort of Nobel prize. There is no rhyme or reason for what the airlines do, but here are some tips for getting good airfares to Europe.
Fly to Spain (Barcelona or Madrid): I am finding some of the best airfares from the United States into Spain. How good? It is not unusual to find a sub-$500 fare from New York and other major cities. So on my next trip to Munich, I am routed through Barcelona. I continue back from Paris. My fare on American Airlines: $680 for Premium Economy. Coach would have been $485. Other good cities to fly into are Edinburgh and Dublin.
Try Premium Economy: Some airlines like Air France are offering terrific deals on their premium economy product. Bigger seats, better food, lounge access (in some cases), and preferred boarding. All for a couple hundred dollars more than being squeezed in economy class. Go for it.
Make a Connection: Once you add a connecting city onto your flight, there is a very good chance the price will go down. This one makes absolutely no sense, but I once priced a R/T non-stop direct flight between JFK and Paris CDG. The price was about $1,100. But if I flew from Boston on the same airline with flights connecting to the SAME FLIGHTS that gave me the $1,100 fare out of JFK, the price went down to about $689. It doesn't make any sense at all, but that's how it often works.