Ask HN: How do you learn about a new industry?

When researching new ideas, I have difficulty with attaining a really comprehensive understanding of a given market. For instance, if I were onto an idea that I think would help out online merchants, how would I go about learning about that industry, about the dynamics and specifics that keep it running, about what would work and won't work?

I find that at best I can achieve a rather superficial level of knowledge and understanding, and I think it's proven damaging in the past when I've steamrolled ahead with developing ideas that eventually floundered.