Hopefully by Week 4, the topic for GC will have been announced and you can start having meaningful discussions with your students. Depending on what the topic is and what level of English your students have, you may have to simplify a bit to keep the students engaged.
How you decide to teach the topic is up to you. However, I suggest you think through this very carefully, as how you introduce the topic and how well the students grasp on will set the tone for the rest of GC.
Our topic this year was "finding the balance between economic growth and resource efficiency"...ooof. I spent an entire class just going over what these words meant before realizing they could be condensed into a much more understandable and researchable topic -- sustainable development.
Class #1
A high-level, engaging, and though-provoking presentation is key in getting students to start thinking about and relating to the topic. I can't provide much guidance here since the topic changes every year, but below are some examples of how I chose to introduce the topic.
I found videos really useful in explaining complex concepts like "economic growth" (and used videos with good subtitles in Spanish).
Class #2
Since the topic is usually quite extensive, you have to balance breadth and depth of your lessons. With intermediate level classes, it will most likely be easier to choose depth so that students have more tangible information they can work with in the mock conference. I chose to focus on the concept of "circular economy" as a means of sustainable development. It was a rather easy concept to simplify while also introducing plenty of new, interesting ideas into the classroom that students could latch onto and form their own opinions about.
The below video was extremely helpful in explaining what circular economy is. It's in Spanish, I know, but sometimes you really shouldn't sacrifice students' understanding of the topic for the sake of teaching in English.