For the past few years, I've seen air fares and trip package prices in general on sale just one season out, sometimes two. Meaning summer fares would be on sale in the winter or spring for summer travel. Unless you are traveling on July 4th week or just after schools let out in your area, wait at least until the the seasonal sales are posted.
No guarantees, but this seems to be the pattern, 4 to 6 months out unless it's a major travel week. International fares seem not to jump all over the place as much as domestic fares do, but they still do change often.