Ask them what they want to know...and it can't hurt by starting with the basisc...let them write a short paragraph introducing themselves...who they are, where they are from, what are their jobs specifics, what are their favorites? hobbies, etc...then, make them come to the front/or in their groups orally communicate their paragrapphs...they can help each other...learn from each other...
with this you can get a feel for their level(s) and move on from there...