Many people in the deaf community may find these terms offensive: "hearing impaired" and "disabled." The terms "deaf" or "hard of hearing" may be more acceptable.
When the exchange of information is complex (e.g., during a job interview or doctor's visit or when reporting a crime) the most effective way to communicate with a native signer is through a qualified sign language interpreter. For a simple interaction (e.g., ordering in a restaurant or registering for a hotel room) writing back and forth is usually okay.
To learn best practices when interacting with deaf or hard of hearing individuals, visit Helping Deaf Patrons