As Espe mentioned, I'd make sure you have the branding idea in place before you even start. It's all about a consistent message. It's about becoming familiar so people trust you. It's about consistency and manners in the things you do, so drive by comment posting and such can affect you negatively as well.
It all starts with questions like, what would my buyers want to know? Why should they want my product or service over someone else's? What is my strong points? And many other questions to be answered honestly as well. Don't lie to yourself, because if you lie to yourself, you'll lie to your customers as well, and that's NOT a good foot to start off on. Once you can answer the questions honestly, then it's time to set out answering them for those reading your message.
Also, consider where you're posting. Guilty by association happens with society. I'd suggest you avoid places that contradict your intended messages. Come up with a mission statement, then follow it in everything you do.