What's the biggest beginner mistake to avoid in Dragonfire?

The biggest mistake: investing everything in what's going to reset, and neglecting what stays forever.

A reminder: with every Reign (8 weeks), what disappears = Reign Level, buildings, research, resources, House level. What stays = dragons, Star Rank, Habits, Gold, Relics, Heirlooms.

So, all else equal, put your energy into the permanent:

1. Raising your dragons' Star Rank (Relics).
2. Upgrading Heirlooms and unlocking their Habits.
3. Keeping your Gold for lasting investments.

The disposable side (buildings, Reign Level) serves the current season, and it's normal to grind it — but it's a re-grind every season. The permanent makes you stronger forever.