By far the most useful thing we did to prepare for the interview was to build a FAQ. The FAQ had everything we thought the partners might ask. For example: * How will we get users? * How do we know users have the problem we're solving? * What's the rocket science? Why can't other people do the same thing? * What existing services exist, and what specifically will make our product better than each of them?

For each question, we tried to have as many concrete details as possible, e.g., statistics, research papers, specific advantages we had over each competitor.

The other really useful thing was to spend about $50 to run a small AdWords/Facebook campaign, and measure the click-through-rate we got with various keywords and ad texts. This let us figure out, 1) did users actually want what we were building?, 2) how many users total could we drive to our site per day?, 3) what is the average cost per user would be? If you're building something that requires getting lots of users, I'd recommend doing this. Just seeing the most popular keywords that are relevant to your product will give you a much clearer idea of what people want.