Outside of the holiday events and some special collabs everything is always there to do.

Do seasonal events at least once while they're available- for example, The Rising event that's on right now won't ever be coming back. But outside of that do your roulettes in Duty Finder once you unlock them for the rewards (resets daily) and check your challenge log for goals that reset every week (you can unlock this feature in Limsa Lominsa).