Not only does it help to be flexible with dates and destinations but being flexible with the route you take is another way to get a cheap flight. Sometimes it’s cheaper to fly to London and take a budget airline to Amsterdam than to fly direct to Amsterdam. There are so many budget carriers around the world that taking advantage of a good deal to another city and then hopping on a budget flight to your destination is sometimes the best way to go. I had to go to Paris once; the flight was $900 USD, but I could fly to Dublin for $600 and get a $60 flight to Paris. It meant more flying time, but the $240 I saved was worth it.
In Google Chrome or Safari, incognito is enabled by hitting Command (or “Control” if using PC), Shift, “N”. For Mozilla Firefox or Internet Explorer, hit Command (or “Control” if using a PC), Shift, “P”. This will open a new browser window where your information is not tracked, thus not inflating prices as you search. Note: if you're using an older version of OS X, open Safari then click “Safari” in the menu bar, and select “Private Browsing”.