In part 1, don't talk about what the most important or best thing is. That is normally the question for part 2. If you look at the example question at the top of this page, it says 'Why would these ideas attract more tourists to the town?' Not 'what's the best way to attract more tourists'. It's a very important difference! Always focus on what the question says.
If your speaking partner is talking about the wrong thing, bring them back to the task. Say, 'that's very interesting but we should talk about why more tourists would come'.