There are no rules for best time to book, it could be a flydrive or even a flight/hotel package 18 months in advance, flight only when released 11 months out or a last minute deal, no-one knows. Just book when you are happy with price and try not to look again.
Check sites in Lee's post, when you are happy with a price either book or post on here all the details and see if anyone can find cheaper or better.