One little corner of (some) websites carry a small price tracker, with an indication of if you should buy now or wait and see if the price for a flight falls.
I have a simple rule: If you have to be somewhere specific at a specific time on a specific date - buy as soon as you can. If the time and date - or even the "where" is flexible - leave it as late as possible.
It helps to understand how the flight pricing system works. Since the dawn of computerised airline reservation systems, airlines have adjusted the prices of seats according to demand. Where an airline knows that demand will be high, there are few, if any cheap (or cheaper) seats; and with the rest of their seats, the price is adjusted in real time, according to demand. This is nothing new. The inclusion of business and first into this same system is relatively new, but still, it is an ongoing and mature system.
At special holiday times, prices will not go down. Indeed, it is very important to book as soon as you know you wish to travel. Relying on price trackers during these peak travel periods is very unwise - you may well find that seats are not available at any price. An aircraft has a finite number of seats; if there are 110 seats and 110 humans are already booked on that flight, then the flight is full and no matter what that little flight tracker may say, you have a problem. Christmas starts when schools finish. The world and his wife start travelling. If you have not booked your trip, you may already be too late.
I have read many blog posts that say there is a good time to buy; a good day of the week or a good time of day. These are all rubbish. Stick to my rule. If you need to be there at a specific time on a specific day, book as soon as you can. If everything is flexible, you can leave it as long as you like.