Добавить «Контроль».в начало свойства и удалите TargetType.Затем в производных от него стилях используйте BasedOn со StaticResource, указывающим на базовый стиль.
<Style x:Key="basicStyle">
<Setter Property="Control.FontFamily" Value="Tahoma" />
<Setter Property="Control.FontSize" Value="12" />
</Style>
<Style TargetType="{x:Type Label}" BasedOn="{StaticResource basicStyle}">
<Setter Property="HorizontalAlignment" Value="Right" />
<Setter Property="VerticalAlignment" Value="Center" />
</Style>
<Style TargetType="{x:Type TextBlock}" BasedOn="{StaticResource basicStyle}">
<Setter Property="HorizontalAlignment" Value="Left" />
<Setter Property="VerticalAlignment" Value="Center" />
</Style>
<Style TargetType="{x:Type Button}" BasedOn="{StaticResource basicStyle}">
<Setter Property="HorizontalAlignment" Value="Center" />
<Setter Property="VerticalAlignment" Value="Center" />
<Setter Property="Margin" Value="2,4" />
</Style>