I am all in for booking as early as you can when you see a nice price.

However, prices can go down when the carrier is offering a promotion. E.g., I booked a ticket this at the beginning of this month with Air France because it was a quite low fare for the summer in July (860EU AMS-NRT), but few weeks later (now), Lufthansa, SAS etc are offering fares for like 650EU for that roundtrip. Kind of bumped, but it does happen that fares go down with promotions, even during holiday seasons. Should have kept my eyes on promotions news.

Though this is for long haul flights. Anyways, +1 for book now.