I have seen several posts that reference Tuesday mornings is the best time to book tickets. It seems to hold true for flights to Cozumel. Another thing we will do is check prices out of Oklahoma City, which is 20 miles from the house, as well as Dallas. Most of the time it is cheaper out of OKC....with a connection through Dallas. Go figure... Check several airports for departures.
I will usually run a Matrix search or Google Flights search, Skiplagged search, and Check booking direct with the airlines as well. We try to book a couple of months out....supposedly 6 weeks is the magic time frame....but we have found cheap flights with as little as 2 weeks before as well.
Google flights and Souhwest have calendars for air fares that will compare prices for the entire month, sometime a couple of days difference can drop the fare considerably.
Some airlines will give you a refund if you call and the flights are cheaper at a given point as well.
Good luck, safe travels.
Jay