Ask HN: Talking to an investor for the first time. Any advice?

Hi HN!

So I am working on a startup part-time this summer, alongside a small group of people (who could turn into cofounders). We don't have a prototype ready yet, so it seems a little early to talk to investors. However, last week an investor at a meetup heard about my idea and really liked it -- we exchanged emails and blocked out an hour to talk over the phone tomorrow.

I am feeling nervous about it because I am not sure what to expect. Except for what I read on HN, I don't have a firm understanding about how the finance end of things work.

Any advice?