If you check airfares from your departure airport on a regular basis, you will soon come to know what constitutes a good price.
I always buy as soon as I find a price (with acceptable times) that I can live with. If the airfare goes down, after you purchase, you can usually get a voucher from the airline for a future trip.
IMHO, if you don't know what you are doing, waiting for a sale can backfire. You could end up paying more or getting times that are not optimal.
You didn't say what airport(s) you are interested in. Perhaps if you post that info, along with your potential trip dates, someone can give you specific advice about prices and the "usual" sale times for the airlines that serve that airport(s).
Good luck!