What should I raise first in Dragonfire to progress?

Master rule: the permanent first, the disposable second.

A recommended priority order:

1. The permanent (crosses Reigns): Stars (Star Rank) via Relics, Habits via Breedmarks + Cores, Heirlooms. That's capital that never evaporates.
2. Concentrate your Legendary (gold) Cores on your key Legendaries rather than scattering them — they're worth +20% stats per star, the best return.
3. Combat XP on high-level beasts and knights to quickly rebuild the level that matters this season.
4. At the start of a Reign, re-grind House Level to reactivate the Heirloom buffs you've already paid for.

Don't sprinkle: one complete dragon (stars + 5 leveled Habits) beats five half-built ones.