The Payment Card Industry Data Security Standard, commonly known as PCI DSS, is a far reaching compliance initiative put forth in a collaborative fashion by the major payment brands (VISA, MasterCard, American Express, Discover, and JCB). These compliance initiatives are overseen and guided by the Payment Card Industry Security Standards Council (PCI SSC).
Thus, if you need to become PCI DSS compliant, there are a number of valuable resources to look at. But first and foremost, you need to understand what Level you fall into for PCI DSS compliance. For merchants, you can be categorized anywhere from a Level 1 to a Level 4. Level 1 audit require an on site PCI DSS assessment, while other Levels you can conduct a PCI DSS Self Assessment. These are general rules, however. Compelling business requirements would require some Level 2, 3, and 4 providers to possibly have an on site audit conducted. Also, there are varying requirements depending on your transaction level between the major payment brands. Find out what your transaction level is, first and foremost.
Additionally, there are also requirements for service providers, thus you will need to identify your transaction level also.