A Safety Management System (SMS) is basically an organization-wide, proactive, and documented approach to risk assessment and risk management. Beyond documentation, a successful SMS is an integrated, everyday part of the entire operation. There is a good deal of information available on SMS from sources such as IBAC and IS-BAO, the NBAA, and the FAA. On the FAA website, look for Advisory Circular 120-92B, "Introduction to Safety Management Systems for Air Operators" and FAA InFO 11010 which provide updates on FAA SMS developments.
SMS in the U.S. and worldwide are rapidly becoming a regulatory requirement, although the timing will be somewhat different depending on whether you are a Part 91 or a Part 135 operator. While the U.S. is somewhat behind some other countries in complying with the International Council of Aviation Organizations (ICAO) mandate, it will get there, with an SMS already required for PART 121 operators by 2018.
Getting educated about SMS will be one of the early implementation steps when you get started. There is an overwhelming amount of information out there and figuring out how to make sense of it and where to begin can be daunting. IS-BAO is a great way to deal with this, as it brings many benefits including an organized approach; but if it is not right for you, a stand-alone SMS implementation can also be done. Advanced Aircrew Academy can help you either way.