Generally, as the teacher, you need to prepare a couple topics for students to discuss in pairs, then they take those ideas to the group and discuss again. If you have a larger class, the groups can report to the entire class.
The teacher will help in the discuss a little, draw attention to any big mistakes or problem areas. You can make a list on the board of new vocabulary that comes up and a list of any sentences students struggle with.
Some good topics are generally local or national news, environmental issues, school, cultural events, food ...
They are beneficial for the students but it's really hard to see progress. I would suggest taping the first few classes and then reviewing them 6 month to a year down the line. Then students will be able to see the progress they have made.
You can find structured news articles on these two sites
www.headsupenglish.com www.breakingnewsenglish.com
Good luck!