Everyone makes mistakes. Especially with things we don't quite yet understand. For every social media success story there are 10 social media disasters. No matter how smart you (think you) are with social media, at some point you will make a mess. But if you start planning your clean up now, you can limit the damage and even gain some respect for handling the situation well.
1. Admit your mistake. Humility and honesty are the only things that satiate the social media mob. Don't try to cover up your mistake, because you can't. Social media is too public and too real-time to ever take back anything you said. Own up to it and you will take away much of the ammunition others would have been able to use against you.
2. Respond directly and publicly to the most vocal objections. Consumers are not all created equal. Some are more influential than others in both supporting and attacking your brand. Invest the time in figuring out who are the loudest and most damaging of your attackers and respond to their complaints publicly in order to leverage that same influence that was used against you.
3. Give people a channel to vent. People will talk, shout and get angry. You can't stop it, and you have to acknowledge that fact. But you can try to limit the extent of the damage. Much in the same way we start containment fires to limit the spread of wild fires, try to get some control by giving people a channel to voice their frustration directly to you instead of to everyone they know. It won't solve the problem, but it might help save the forest.
4. Do something right. It's human nature to extrapolate a single occurrence into a generalized conclusion. Don't let this one social media mix-up brand you as a social media ignorant. Do something right, and do it now.
5. Don't make the same mistake again. Whatever mess you made will eventually pass (and hopefully quicker now that you are prepared). But don't think that just because you cleaned up the milk the jug is now spill-proof. Analyze what went wrong and why. Learn from your mistake so you never make it again.