As a credit card-processing merchant, you are required to complete an annual self-assessment questionnaire and quarterly network security scans through a PCI-approved scan vendor to demonstrate compliance.
Keys to PCI compliance include the proper network security, careful handling of customer cardholder data, and the use of only PA-DSS-validated POS and payment processing systems.
The PCI-DSS standard contains 12 steps to compliance.
For the details, find out more at: https://www.pcisecuritystandards.org or http://www.pcicomplianceguide.org/aboutpcicompliance.html.
You can also learn more from these articles from SpeedLine’s PCI auditor, Coalfire Systems:
PCI Primer for Restaurateurs
10 Common PCI Myths