People often ask me this, and the answer is simple. Yes, you want to broadcast some messages relevant to your product or service, as this will increase your search engine rankings, but you need to mix it in with some run of the mill chitter chatter too. It’s called social media, so it’s important we keep it social.
Join in with other people’s conversations, answer questions and re-tweet others who have posted something of interest. Make general day to day comments; the kind of mundane conversations you’d have with the person standing next to you in the supermarket queue.
Don’t over-think Twitter – it’s just a conversation. For most people you can just tweet what pops into your head. People will forgive your spelling mistakes and bad grammar – as long as that isn’t a part of your service, e.g. if you’re a copy writer your tweets need to show your talent. If you manufacture widgets, the fact that you’ve missed a comma or mis-spelt a word really isn’t the end of the World.