In general the rule about airfares is that they're illogical and unpredictable. The way not to go crazy is to view them a bit like playing the stock market: You never really know which way they'll go, but most of the time they go up.
Sales or special offers are just one particular variation on this.
If you already know that you're definitely going and when you're going, then book the best deal you can find as soon as you decide you will go. And then don't look back. It is possible, but not particularly likely, that prices will drop after you book, but it's not worth regretting if they do -- they might just as well have gone up.
If you haven't yet decided that you will definitely go, you can bide your time -- and then pounce if you happen to see a deal so good that it makes you decide to go. Then, again, don't look back.
Beyond this, there's not really any general advice to give you. How you make your decisions (and which deals might make you decide to go somewhere you were not sure of) depends on things only you can decide: How badly do you want to go there; how large is your budget; how risk-tolerant are you? You could hold out for a better deal, but the risk is that the price might only rise to the level where you can't afford it at all.