Think of something you are really good at, or really interested in – perhaps a hobby, a skill, or even an area of knowledge.
Imagine you have just met someone who is interested in learning more about it.
Give an overview first (general introduction), then describe your hobby/skill/knowledge in detail.
If you can find someone to ask you questions, all the better!
If you are using this topic in a conversation class, set a time limit of 15-20 minutes for pairs to discuss their expert interests, then change partners.
I’ve been getting deep into DSLR photography, after upgrading from my old Powershot point and shoot, in order to do some professional photo shoots.