Hi. It seems that you are asking if it is natural to make your students aware of the fact that you are teaching them how to have group discussions. It is natural to make them aware that this is what your doing if topic is on your syllabus. If it is not on the syllabus and you are simply wanting your students to learn more effective group discussion techniques, because you noticed their need, I would not make them aware. I would simply divide them in groups with clear instructions on the topic that you would like them to engage. Then I would would visit each group to see how the conversation is flowing. If it is not flowing well -- meaning that there are long pauses of silence etc. -- I would give them suggestions on how to move the conversation along. Then I would leave the group while they apply your suggestion. For example:
Teacher: Break into groups of five and discuss 5 ways to make the world a better place.
Students #1: We can make the world a better place by being kind to others.
Student #2: We can make the world a better place by not wasting resources.
Student #3, #4, & #5 -- No answer -- silence for 2 minutes
Teacher: I could give away old clothes. What are some things that you could give away or do without that might make the world a better place? (teacher walks away to give the students a chance to inventory their belongings that could be given away for the cause).
I hope I understood your question and that my answer helps.