There isn't much there, unfortunately. The key is that the view model should not know _anything_ about the exact presentation of its content.

As a thought exercise, you should be able to use _one_ view model for:

 1. OS X
 1. iOS
 1. Windows
 1. CLI
 1. Web

In practice, there are other things that make this impractical (like different information levels per platform), but the general idea — "Don't tie your VM to your specific presentation, or even UI framework" — is helpful.