Check your work. Most wheels are imprinted on one side with the brand or model. Before rotating wheels, the imprinted sides should all face the same direction. After rotating and flipping your wheels, the imprinted sides should all face the opposite direction. Bearings Prevention ins the first step in bearing maintenance.
Prevention means skating clear of puddles and sand.
Water and sand are the archenemies of bearings. If your bearings don't spin freely or make grinding noises, it's time to service or replace them. Serviceable bearings have removable shields and c-clips. Non serviceable bearings are like disposable cameras. Once they're used up it's better to buy new ones.