I prefer to switch groups every week. So they can work with different types of personalities. They will have an idea of diversity in the field.

I think a good way to start with your new class is giving a non-graded quizz and discuss it with them the results. With this, you will show them that you worry if they learn or not, that you want to know their skills and knowledge.

I think a good way to keep students with you during lecture day is sharing with them videos and documentaries, of course updated. Inclusive, adding these links to the presentations will be more exiting for them. You will have a great class participation as an outcome of this.