Like most things in travel there isn't one sure fire answer to finding great award availability.
That said, most airlines open seats up about 11 months prior to flight date. Generally flights will have a couple of low priced award seats on these dates. So if you're a planner (like me) mark your calendar for that 11 month window.
Otherwise airlines generally open up space quite close in, within a month. That can be a bit nerve wracking, but most domestic carriers now let you cancel for free so it can be worth holding a flight and waiting on a better option.
In between those dates I suggest you look regularly 1-2 times a week to try to find the right award space.
The number one tip here is award space is LIMITED. When you see a good price (in miles) grab it, especially for business class. Don't wait a day or two it will most likely be gone.
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