The role of Twitter for small businesses is evolving and changing fast, but there are now a handful of very good Twitter guides out there. Below are four of my favorites (including two specifically for the real estate industry):
DuctTape Marketing’s “Using Twitter for Business“
Flyt’s “How To Use Twitter for Business“
Real Estate Tomato: “Twitter Explained for the Real Estate Blogger“
AgentGenius: “Social Media for Real Estate 101: Twitter“