Unfortunately there's no reliable formula for picking the "best" time; they like to keep us guessing. The general advice is to monitor prices and when they are something you like, buy the tickets and then stop looking at the prices.
Caribbean destinations seem to feature in sales reasonably frequently - but these are usually for flights outside of school holidays.
Depending on how you want to do when you get there it may also be worth looking at Virgin Holidays as sometimes - not always - a package price for flight and hotel can yield overall savings. That was certainly the case when I priced up or summer holiday this year.
Paul
We can get better, because we're not dead yet
