YES, good water quality is a must, it prevents any nitrate related diseases and hole in the head, which oscars are prone to. Get into the habit of weekly water changes of about 60%. It can seem like a burden, but think of it as allowing your fish to breathe in fresh air, and not in a musty old closet. Stay away from feeder fish. Use several good quality pellets and feed frozen or dried shrimp several times a week. Crickets and earthorms are great also. A variety of foods will make an oscar very happy. Keep the temperature about 80 degrees.
Rember this and the advise of others, and you oscar will be as good a pet as any dog.