1.Follow the recommended practices for managing the physical OS, e.g , time synchronization,log management,authentication,remote access etc.
2.Install all updates to the guest OS promptly.ALL modern OS's have features that will automatically check for updates and install them.
3.Back up the virtual drives used by the guest OS on a regular basis,using the same policy for backups as is used for non-virtualized computers in the organization.
4.In each guest OS,disconnect unused virtual hardware.This is particularly important for virtual drives, but is also important for virtual network adapters other than the primary network interface and serial/parallel ports.
5.Use separate authentication solutions for each guest OS unless there is a particular reason for two guest OSs to share credentials.
6.Ensure that virtual devices for the guest OS are associated only with the appropriate physical devices on the host system,such as the mappings between virtual and physical NICs.