One thing I did was sign up at bing travel. You enter the info for where/when you're going & they send you updates every day with a projection of whether to buy now or wait. It really helped me let people know when they should book.
To answer your question, though, we booked our travel in like November for a May wedding, way in advance but we did get a good deal.
Cheap flights, hotels, destinations - Bing Travel
good luck!