Open the file you want to apply the soft focus effect to.

Copy the background layer twice (Keyboard Shortcut is Ctrl+J) and rename copy 1 to "darken" (double click the name on the Layers palette to be able to change the name).

Turn this layer off. Click the eye icon to the left of the image on the Layers palette. To turn a layer back on, click the box where the eye was originally).

Rename copy 2 to "lighten".

On lighten layer:

Set blending mode of Lighten layer to Lighten (there is a box to the left of "Opacity" near the top of the Layers palette. Click the down arrow to get the drop down menu, and select Lighten).

Apply Gaussian Blur to the lighten layer (Filter > Blur > Gaussian Blur). Experiment with number of pixels you use when setting the blur effect. If working on a portrait, try using a pixel amount that is equal to half the diameter of the subject's iris. (I select the default brush and place the brush over the subject's eye - there are other ways, but this works for me. The brush will be a circle, and I adjust the size to fit the iris, and then I read the diameter of the brush to know how much Gaussian blur to use.)

Set lighten mode opacity to 60%.

Turn off lighten layer.

On darken layer

Set blending mode to darken.

Gaussian blur = XX pixels. Experiment with an amount about half of that used in lighten layer.

Set darken mode opacity to 40%.

Put both filters together

Turn on the lighten layer.

Turn off background layer.

Make new layer, name it Soft Focus, click the icon immediately to the left of the trash can icon on the Layers palette or from the menu bar: Layer > New > Layer.

Merge darken and lighten layers into new Soft Focus filter layer by holding down the control and alt keys while choosing "merge visible" from layers palette fly out options menu (hold the Ctrl and Alt keys down and click on the arrow on the Layers palette, highlighted above, and drag the cursor to the Merge Visible selection in the fly out menu - be sure to hold down the Ctrl and Alt keys throughout the drag operation).

Turn off lighten and darken layers.

Turn on background layer.

Add a layer mask to Soft Focus layer (The layer mask icon is at the bottom of the layer palette.  Click the icon and it will add a layer mask - see highlighted areas on the Layers palette below.)

The layer mask in the example is filled with white.  If it is filled with black go to
Edit > Fill. Then, in the Fill Options box that opens up use:
Use: White / Mode: Normal / Opacity: 100%

Enlarge face (use the Zoom tool, i.e. the Magnifying glass).

Set the foreground color to Black (Keyboard Shortcut is "X").

Set the brush color to black.  (Keyboard Shortcut  "X" to exchange background and foreground colors).

Choose the Brush tool (Keyboard Shortcut is "B") and select a size that is convenient to work with for the areas that need to be brushed.

Change the opacity of the brush to 50%.

Brush over eyes and eyebrows (You can soften brush effect by holding down shift key).

As you paint in the layer mask with a Black brush you will see the image in that area become sharper. Where you paint with White you will see a softer image.

If you paint with Black and sharpen too much of the image you can simply switch to a White brush and paint back in the soft effect. 

Adjust the opacity of the soft focus layer to increase or decrease the effect.

Retouching hints

The eye that is further away from the camera can be a bit less sharp.

Sharpen lips, edge of nose and maybe the nostrils.

Lower the opacity of the brush at the edge of the sharp/unsharp areas while you retouch. This will make for a smoother blender of the effect in the final image.

Turn layer mask on/off by holding shift key and hitting layer mask.

None of the amounts (Gaussian blur, opacity, etc.) are set in stone. Experiment with them and have fun retouching your images.