Call the person by his first name, if he so prefers it. It helps you get his attention and as a sign of respect, address him according to the profession he was once engaged in, such as Doctor, or Sir or Ma’am if he were a serviceman. Speak slowly using simple words in short sentences. If, at first, he does not understand what you were saying, repeat it over again using the same words as when you first said it. You may use hand gestures or other body languages to reinforce your words.