From an industrial viewpoint, the best way to prepare for a Cal-OSHA inspection is to have an effective safety program already in place. Everyone in the company, from the CEO down to the newest employee, should buy into the program. Plan means to review regulations for applicability, perform a gap analysis, and develop the written programs to meet the requirements while involving employees in the process. Do is implementing the programs, conducting training, and improving awareness. To check, you must audit and inspect your facilities.
Act denotes acting on the findings and addressing any shortcomings.
When Cal-OSHA arrives at your site, it's important to be honest and cooperative with the inspector. Understand that Cal-OSHA has a right to be there and inspect the facility. If you were to decline entry initially, the inspector could then go retrieve a warrant and return for a more thorough search. With your cooperation, the inspection could be short when there's a limited scope involved, such as an injury investigation. In addition, Cal-OSHA has the right to interview employees on company time.