Add a layer mask (by pressing the third button on the lower part of the Layers Palette) to the layer you have just blurred and fill it with black. Then pick a soft, medium sized brush and start painting with white on the layer mask. Make sure you avoid any lines on the face; use it only on the skin, to get a smooth, professional effect. Vary the brush size and opacity depending on the area. Avoid blurring the eyes, lips or hair.