Create soft focus - Method 1

Step 1 - Open the photo
If it isn't already open, open the photo you wish to work on.
Step 2 - Duplicate the Background layer
In the Layer Palette, duplicate the Background layer. The duplicated layer (named "Copy of Background") will be the the active layer.
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Step 3 - Adjust the Brightness and Contrast
Choose Adjust > Brightness and Contrast > Brightness/Contrast. In the dialog, set the Brightness to 35 and the Contrast to 20.
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Step 4 - Apply Gaussian Blur
Choose Adjust > Blur > Gaussian Blur. In the dialog, set the Radius to 4.
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Step 5 - Reduce layer opacity
In the Layer Palette, reduce the "Copy of Background" layer's opacity setting to 50%.
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Step 6 - *Optional* Reveal Non-blurred layer below
*Optional* With the Eraser tool, drag over parts of the blurred layer to reveal the non-blurred layer below.
Notes and Tips:
Unlike the Method 2 Quick Guide of the same name, this yields a similar effect while utilizing multiple dialogs and program features. This exposes you to more of the application, enhancing your learning experience.
If you perform Step 6, try setting the Eraser tool's Hardness value to 20 or less.
For a fun experiment, try this Quick Guide with photos consisting of different light sources and contrast values.

Learn More:
Create soft focus - Method 2
Create depth of field
Modify a photo via blend modes