Start off by downloading and reading this e-Book provided by the Payment Card Industry (PCI)

Then read the following e-Book provided by VeriSign to understand why companies fail their PCI Audit:
http://www.verisign.com/static/PCI_REASONS.pdf

Afterward, you should understand everything you need to!

Better to read current version of standard (v.1.2). Link included in previous answer points to old version. Latest version includes the audit procedures also.

Goto https://www.pcisecuritystandards.org/ for latest version, reference guides and guidelines.

You should start as follows: - make sure you know where you store and handle credit card numbers - draw a network map which shows the apps, databases and data flow - fill in the PCI self evaluation form - read the standard in order to understand where biggest gaps are

Here is the process I follow: 1. Identify in scope devices. 2. Conduct a gap analysis - internal and/or external audit against standard. 3. Remediate gaps. 4. Lock down the environment for four (4) weeks 5. Prepare for audit. 6. Conduct PCI-DSS audit - by a QSA 7. Remediate remaining gaps. 8. Auditor to submit RoC.