MVVM is coding pattern that I like a lot. There’s a lot of people who say it isn’t so good but for Windows Phone and Windows 8 coding I find it perfect. MVVM comes from Model - View - ViewModel and the main idea is to separate data structure, logic and views.
I have found it especially powerful when creating application that in future will be ported to another platform/updated. Example when you are creating WP8 project you might want to port it to Windows 8 too in near future. Also if you are friend of Data Binding then this pattern is totally for you!
MVVM Light Toolkit is package that will help you get started with MVVM very easily and very fast. So if you want to get started with it just download it from codeplex or get it from NuGet and here is great starting point in your journey into MVVM.