The same way we do on every site.
As users, you do have power over the problem (should one arise):
Vote early, vote often Both down and up votes help those not yet in the thick of things see what the community deems acceptable and unacceptable. Additionally, it helps the most-positively-contributing members rise in reputation (while holding back those with dubious records) so that they can do more to make/keep the site great.
Flag the trolls, don't feed them Rather than arguing with a troublemaker (which only encourages them), just use the "flag" link to let mods know that a question/comment/answer requires their attention. This way the problem is dealt with, and the troublemaker's behavior isn't reinforced.
Vote to close The longer a bad question hangs around, the more emotionally attached its proponents get, and the more resistant they are to fixing it. When you see a question that meets the close criteria, vote to close immediately -- it can always be re-opened if/when it is fixed.
Teach newbies the ropes Once new users are able to find this site, their early experiences will shape how they see the community, as well as if and how they will participate in it. If you notice that an apparent troublemaker is a newbie, take the time to leave explanatory comments regarding edits, votes to close, and so on, as politely as possible. The better you treat your newbies, the stronger the contingent of positive, sane, active contributors to this site will be.
Focus on the content, not the person behind it The best way to get people to take direction with regard to learning the format and behaving properly is to have an environment where people don't take reactions to their content personally. If your community bickers about every down-vote, or whines about who's chatty comments were/weren't scrubbed, you create an environment where users take every suggestion as a personal affront, and nobody wants to improve. Both in giving and receiving criticism, be as gracious and generous as possible, and you'll find that everyone is more inclined to improve their posting habits and help others do so, too.
Lead by example The absolute best way to make this site better, and defend it against an influx of garbage, is to be even more exacting in your standards on your own posts than you are on others'. If a significant minority of the posts to a site are above par, the overall site standards tend to slowly creep up closer to that example.
If things get really out of control, there are moderators and the Community Team here to help.
We have Top Sekrit Mod Toolz (TM) that are available to diamond mods and those with enough reputation that help us keep track of ongoing problems.
If someone appears to be cluelessly abusive we try to educate them, if that fails (or they were apparently purposely abusing the site) we move on to timed suspensions. If there's a problem that mods need help with, or if a user needs help understanding the process or wants a second opinion, they (mods, user, random guy down the street) can contact the Community Team (community -AT- stackexchange -DOT- com) with any concerns, and we'll turn our very experienced eyes (and possibly brains and/or magic wands) on to the problem.