Hi Daniel,
If you want your entire window to render scale up uniformly, you could apply a ScaleTransform to your Window's root element's LayoutTransform property.
Alternatively if you want to handle controls individually, making apps more touch friendly generally revolves around using a larger font size, sometimes larger icons, and increasing padding on controls.
For instance in the Browse for Folder demo, you could apply this style:
<shell:ShellTreeListBox x:Name="treeListBox" Grid.Row="1" Margin="0,5,0,10" RootSpecialFolderKind="Default" IsNewFolderContextMenuItemAllowed="True">
<shell:ShellTreeListBox.ItemContainerStyle>
<Style TargetType="grids:TreeListBoxItem">
<Setter Property="Padding" Value="10,7,15,7" />
</Style>
</shell:ShellTreeListBox.ItemContainerStyle>
</shell:ShellTreeListBox>
Also update the Buttons to have more Padding, and possibly increase the FontSize of all controls if appropriate too.