In the SF bay area, with all of my theaters on the non-profit season subscriber model, I tried to pay attention to season announcements when they came out in the January-March time frame. Then, using my knowledge of each theatre's production timeline, I'd try to plan out a season of shows I was a good match for with as few gaps as possible. When I started out, I would have three or four plans worked out. I'd then market myself, in as narrowly-targeted a manner as possible, to the shows I'd identified. Over time, as I developed working relationships with some theaters in the area, this process got pretty streamlined. Usually by May/June, budget issues had been worked out and I had at least verbal agreements with shows from September-June of the next year.
Knowing what scale was, I could then budget out my income over the course of the season, and save up money from the large contracts to subsidize the smaller contracts. I'd also carefully track my projected health weeks to make sure I wasn't in danger of losing coverage.
My career goals included avoiding out-of-town shows; providing a predictable base of income for my family; and working my way up the available levels of contract. Planning family vacations months in advance was also a boon for booking so far in advance.