So many brands jump in to social media without any idea of what they are going to say or how they're going to say it. The results aren't pretty--many companies give up and leave their accounts abandoned, others keep on going but you wish they would give up because it's embarrassing to see how badly they are doing.
Today i have a a nice review of good, bad and the ugly examples of brands on Twitter. One of the best, in my opinion, is Orange whom i think they: " really tweet like a person and someone who cares." And that is the important point. If you are going to engage your audience via social media, you need to act like a human. You need to be empathetic, interesting and interested and capable of having a conversation about your brand without bragging, spamming or talking like you are a press release.
Ask yourself: What would a human do? And do that.