Tavern contracts
The tavern is the game's baseline: the thing you can always do, that always pays, and that never requires you to be online at a particular time. Contracts are timed rather than instant, which means the tavern's real currency is not gold but the decision of what your character is doing while you are not looking at it.
How it works
Contracts are grouped into level-gated areas, and each one costs energy to start and finishes on a timer. The fight itself runs through the same simulation as everything else in the game, so a contract you fail is a build problem rather than bad luck, and one you clear comfortably is a signal you can afford to move up an area. Energy is the limiter and it refills over time, which is what stops the tavern from becoming the only thing anyone does.
Best practice
Use the tavern as your test bench. A contract is a known, repeatable opponent, which makes it the cheapest way to find out whether a gear swap or a new pet actually changed anything before you spend a dungeon cooldown finding out. When you are unsure about a build, run the hardest contract you can reliably beat and watch which round the fight turns.
The common mistake
Treating a full energy bar as something to protect. Energy regenerates whether or not you spend it, so a bar sitting at maximum is not savings, it is regeneration you have already thrown away. Spend down to a buffer and let it refill while you do something else.