Those of us who are already familiar with other Stack Exchange sites know that we can vote to close a question if it is off topic or not a good fit for the question and answer format. I've been deliberately asking some questions that are borderline off topic in order to see where the community draws the line, but even when I've continued to push beyond what I consider even vaguely on topic I have seen very few votes to close.
We need everyone to be aware of the ability to vote to close before we move to public beta, so that everyone can contribute to closing off topic questions before they become a problem. In public beta there will be more people using the site and therefore more off topic questions, so we need to get the hang of this now.
This is mainly just to encourage everyone to start using their vote to close option, and to mention it to others who may not see this meta post, but it can also be a place for discussion/advice about any subtleties of how to use the vote to close / vote to reopen system. My guess is that we have quite a lot of people who are new to the Stack Exchange format so we need to actively encourage people to use their open and close votes (not just up and down votes), and emphasise that voting to close is a positive thing - a question can still be reopened once it has been edited to make it on topic.