In general, there is no need for anything special to prepare with respect to how security controls are managed on a day-to-day basis. Remember that a penetration test is a point in time review of the environment. The test is going to assess the security posture at that particular point in time. If patches are deployed every Wednesday, for example, there is no need to change this behavior to accommodate the penetration test itself. If the results of the network penetration test determine this process requires attention, then that would be the appropriate time to adjust.
An organization should expect to participate in preparation activities related to planning the penetration test itself to ensure the test can be performed under controlled conditions. Some preparation related to positioning the tester may also be needed, specifically when testing is being performed onsite.
The hiring company should be prepared to participate in the planning and coordination activities and be ready to have documentation available that details the in-scope IP ranges for testing when pen testing is being performed. Also be ready to prepare test environments and to support test scenarios defined in the scope. During internal onsite network penetration tests, oftentimes visitor access badges are required for the penetration testers. Otherwise, there is not much else that is needed to be done prior to the test.