What is the most effective way to demonstrate being prepared for an interview?

To prepare for an interview, find out as much as you can beforehand. Call the person who scheduled your interview and ask:

Who will you be talking to? Will you meet the manager you'd work for, or will you just talk to HR? What are the interviewer's expectations? What's the dress code? Dress better than suggested. Most times, it's best to wear a professional suit. You'd be amazed how many candidates show up looking like they're going to class, not presenting a professional demeanor. Get directions to the office. Plan to leave early. Keep a phone number to call if you get stuck on the bus or in traffic. If you arrive late and stressed, the interview will not go well. If you don't have a detailed job description, ask for one.

That's a five-minute phone call.