The world opens in a rough order, then branches. Respect the branch you take.
The early line
The Mines teach reactions. The Coal Pits add enemies that punish a careless wand. Clear both slowly; the loot is steady and the danger is readable.
After the branch
Past the early biomes the path splits. One way is harder but richer, the other safer but thinner. Pick the safer path when your wand is still weak.
Where to farm
Farm where you win without thinking. Chests and calm enemies give gold and flasks. A hard biome you survive by luck gives less than a calm one you clear twice.
Reading a biome
Before you commit, scan the entrance. If you cannot name an escape route, do not go deep yet. The next biome is reachable once your wand fires without locking up.
Know the danger curve
Biomes escalate from the Mines through the Collapsed Mines, Snowy Depths, and Underground Jungle, each adding new enemies and hazards like exploding barrels and lava. Go down only when your wand chains reliably; falling behind on fire rate gets you walled at the first Wand Mech.