Simply enjoy the conversation, ask them to tell you about the biggest challenges in their business, and most people will open up and give you some of the most valuable feedback you can get as an entrepreneur. It's much more valuable than sitting in your basement and running an Adwords campaign to a landing page. The depth, richness and quantity of feedback you get might surprise you. You might even consider asking your prospect if you can publish a transcript of the interview on your blog.
Publishing your customer development interviews (with your prospects' permission) will give you near instant content for SEO (get it transcribed with SpeechPad if you like), added value in the form of information for other prospects in the industry, and insight into how they express their pain points that you can inject back into your pitch and marketing messages.