You can SEARCH for this in the SEARCH BAR as this topic is brought up VERY OFTEN.
We go to Europe yearly and we typically have the best luck when we buy on OPENING DAY -- which is 330 days from your return trip home.
We are going to Europe in December (which we go almost yearly for the Xmas Markets in Germany & Austria) - and we bought our tickets on opening day back in February and we got Into Munich and out of Amsterdam, Business Class for $1278. Now, you can't even get COACH class for that for those dates.
We are going again in April 2024 and we bought tickets in May -- Into Zurich, out of Amsterdam - Premium Select for $1260, Coach was $920 at the time. Now, when I just looked, Premium Select is $2076 and Coach is $1114.
We are going to Italy in Sept 2024 and we will look at prices on our opening day which will probably be around Oct/Nov. We know what we typically pay, so we buy when the price looks 'acceptable' to us. It's always a gamble and a risk.
My good friend is a Travel Agent with AAA and she always encourages us to buy EARLY to get the seats we want and she says the price is 'usually' better earlier.
You do risk flight time changes by booking early, but it's never been an issue for us.