We’ve talked about the Windows Phone Design Grid before so I will keep this post short. The key is to leverage the Grid for composing your Windows Phone UIs. The Grid has a 24 pixel margin to left and right. Always respect that margin. Then you have 25 pixel columns and 12 pixel gutters. It’s always best to deploy UI objects from within a 25 x 25 cell. Take a look at the Layout and Composition in Windows Phone posts in this same series to get a better idea of how to use the grid.
Windows Phone Grid Basic Cells in PNG (Transparency - great for Expression Blend)