I pretty much always have a google flights price alert for one way fares to and one way fares from EIS (ORD home airport). When I book a trip I add in the exact dates and set a second search. I get an email every day from google with the lowest fare known at this time AND the lowest fare for my journey. I typically will track each direction separately. As one leg will go on sale and then a few weeks later the other will.

I end up having my tickets booked about 8-12 weeks out from the trip. If you know whats cheap, you can act when the price is right. American is usually the cheapest going down island and United is usually the best (almost cheapest) going home. I avoid STT like the plague unless ridiculously cheap, which does happen from time to time.