The off-season is pretty much here for most triathletes, a few may have a late-season Ironman, but even the time until those is not long, and the off-season will begin.
Athletes tend to be pretty good at setting goals for the season, but few really set goals for the off-season. Off-season goals can really help to motivate and provide the big break-through the next season.
What types of goals should one set? This depends on the athlete, but usually, the off-season is the best time to work on weaknesses.
What weaknesses do you have as an athlete? Chances are you are fit, but lack the top end speed needed to race at a higher level. This should be your focus and where you set your goals. For some, this means training for a new 5K PR, while for others it might a new mile PR, in terms of setting goals.
It could also be a goal time in the pool, for the 400, 100 or 50, or perhaps even doing fly for a full 100 or 400.
On the bike, athletes can set a CP 1 or CP 6 wattage goal, or even a goal time for a shorter local climb in their area. Another opportunity is in cyclo-cross, racing a local series, with a placement goal for the series.
You'll notice these are sport specific goals, and not related directly to triathlon performance, but rather indirectly. The time frame of these is much shorter than what triathletes will do on race day, so it is general preparation, not specific. Periodization is basically the idea of going from general preparation to specific, in phases of time, changing the training stress to more closely resemble the demands of race day.
For most triathletes, race day is aerobic, so aerobic work is more specific, whereas super intensive, neurological training is more general, and what most triathletes need to train. But many get stuck on the same habits and workouts, performing a lot of race-specific work in the off-season. Then when the specific period of training comes, they are not introducing a new stress, so the body is not responding to it, instead plateauing and showing no improvement for the athlete.
Sit down and set some specific, measurable goals for the off-season, which address your weaknesses, and bring a new training stress to your body.