<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" AllowDrop="True" >
    <Grid>
        <Label AllowDrop="True" Drop="UIElement_OnDrop" DragOver="UIElement_OnDragOver"></Label>
    </Grid>
</Window>

private void UIElement_OnDragOver(object sender, DragEventArgs e)
{
    e.Effects = DragDropEffects.Copy;
}

private void UIElement_OnDrop(object sender, DragEventArgs e)
{
}