Build, sharpen, taper.
Ayers doesn't suggest veering from the classic competitive runner's mantra, and he says that most ultrarunners make running a "seasonal experience" – that is, they train year-round but consciously prep to be at peak form at certain times of year. While Ayres himself runs a few races a year, and other experienced ultrarunners might even do 10 or 12 races annually (making some races a part of their training), he suggests starting yourself out with a limited goal.
"For someone who hasn't run an ultra before, I think having one target date is extremely useful. Plan to make your training a great adventure with that one race in mind." From your target date, count backwards, allowing a couple weeks before the race for a "tapering" period and two or three weeks before that for a "sharpening" period of speed work. Greater detail and recommendations for these types of workouts can be found in his Notes for an Aspiring Ultrarunner in 'The Longest Race.'