Great info in this thread. One thing I'd like to mention is you need to know what regions fill up fastest. For example, Europe on holidays/summer goes relatively early, as does Hawaii over the holidays.

You can often book Asia on United without much warning, even for the holidays, but not Hawaii/Europe.

It might be different on AA or Delta (I think everything is tough there). But with that said, as soon s you can narrow down date/location, book!