Upgrade your tavern in order to get better gladiators. The higher its level, the more upgrades it will unlock. Use your free refreshes as often as possible to maximize the potential list of gladiators that can be recruited.

Look for the gladiators with the most potential in the tavern. They are ranked from E (the worst) to LEG (legendary, which is the best). Choose the highest rank or wait for the next refresh. The better their stats, the more Aureus they will produce and the faster they will level.