The first time discus owner should never mix discus with other fish. There are just too many potential problems. You should get to know and provide the discus with their best possible environment.
That being said, the only cichlids I would ever mix with discus are dwarf species. Certain of the tetras (cardinals, rummy nose, black neons), do make for the perfect tank mates when kept in schools of 6 or more. Likewise clown loaches and corydoras make for a good clean up crew.
Discus are best kept in groups of 5 or more. A minimum of 55 gallons would be required for 5, and no other fish.