Many GMs - myself included - like to begin a campaign with a "Session 0": a session where the ground rules of the campaign are laid out plainly before any actual play begins. Some topics of discussion during this session require little tact; things like the campaign setting and rule variants fall into this category. Others, however, are not so easy to address.
One such topic is that of the participants' expectations. Ideally all participants' playstyles, character goals, and metagame desires coincide in a way that helps the campaign run smoothly and ensures that all involved enjoy it. In practice this is rarely the case, but a well-crafted Session 0 can draw the participants as close to this ideal as possible. With that in mind...
What strategies can be employed by a GM during Session 0 to help ensure that campaign participants' expectations align?