#4: Using it as a push marketing channel
Most marketing people create a "message" and push it to multiple distribution points. That tactic does not work well in the Twitter ecosystem. While using Twitter to push press releases or automatic distribution of an RSS feed from your company blog might be appealing, the consumption model is minimal. Only linking to your website in your tweets will quickly become boring to your followers.
When you have people follow you, they follow for a reason. They have effectively "opted in" to hear what you are publishing and sharing. Focus on adding value and giving them what they want. Use this channel as a way to communicate industry news and trends -- insights that are valuable to your target audience. Interaction is the key to building influence on Twitter. Share openly and don't only talk about your services. Find a way to mix it up and be interesting and human in your interactions.
Tip: Focus on adding value to the people who matter most and you can't go wrong.