The best way to back up a virtual machine is by installing the Zoolz/BigMIND desktop software inside it and configuring a backup from there, treating it as a physical machine.

You can also set scheduled snapshots creation within the virtual machine’s software. Then, use the Zoolz/BigMIND desktop software that is installed on the hosting physical machine to back up those snapshots.

As an example of how to create snapshots on VMWare Workstation, click here, and for VMWare Fusion, click here.