A lot of travel and airline companies practice 'dynamic pricing' they monitor how many people are looking at a particular flight, and the price rises the more people who are looking at it. So avoid searching when everybody else will be, I.e Saturday and Sunday, when couples will be making travel plans together. They an odd time, like Tuesday evening for example. The poster above, booked on Christmas Eve. How many people will be searching for flights then?
Also, do a search on your work pc or smartphone before deciding. Once you start searching on your home PCs, the company will log your IPS (the identity of your wifi) and will know exactly what you are searching for the minute you type in the web address, and will probably raise the price because the program knows you definitely want that flight and wants to extract as much money from you as it can.
If you have a frequent flyer membership, log in using your profile, take the booking right to the payment level, then close the browser window. Within a week you will get a 'special offer' email from the company which looks like a mass mailing, but in fact will be tailored for you; they want that sale!
I will often go to my favourite airline in a fanciful mood, just to price up my dreams. I always get an email a few days later with 'special offers' to those destinations. This year when booking our flights, I left it a week after looking and lo and behold, I received a special offer email. DH and I saved £750 each on our flights, a tidy £1500 between us. They play on people's holiday excitement and desire for instant satisfaction.