Determine the amount of Sharpness:

Because you will later hide all areas that become oversharpened, you may set the sharpening Amount and Radius to a level that sharpens to the maximum required by your image.

Using the Amount and Radius sliders, you will see a preview in the Unsharp Mask Palette, showing you the results of your choices. You can also use the little 'hand' in the Unsharp Mask Palette window to navigate around all areas of your image.

But don't worry, if you press Enter to make a choice and then afterwards decide that it was not right, you can just press "CTRL Z" or CTRL ALT Z" (Command Opt Z on the Mac) to undo your selection and start over. Whenever I'm unsure, I always press Enter to make a selection so that I can see the results on the actual image. If it is not what I want then I quickly undo it by entering the CTRL ALT Z shortcut.

After you have chosen a level of sharpness and added it to the Duplicate Copy of your image, the next step is to mask out the unwanted sharp areas.

Understanding and Using Layer Masks:

Now you will make a layer Mask (relax, it's completely easy):

A Mask's function is to hide and reveal portions of the image on which the mask is placed. It is exactly like erasing, but much better because nothing you do to the image is permanent. Masks allow you to 'magically' erase and reveal to your heart's content. You can continue to change your mind and change your choices, just by painting on the mask in either black or white, or any shade of gray (which changes the opacity). Once you get used to the concept of Masks, I guarantee you'll rarely use the Eraser Tool again, which erases permanently, which means you have to live with your choices.

OK, now that you understand the beauty and magic of Masks, let's move on to the next step:

Another way to select a Layer Mask is by going to your main Menu Bar and Choosing: Layer, then 'Add Layer Mask'. Whether you choose a 'Hide All' or 'Reveal All' Mask doesn't really matter, both will end up with the same results once you're finished.

But for the sake of clarification, you could choose a 'Reveal All' Mask (white) if there is only a small amount of sharpening you wish to hide or you could choose a 'Hide All Mask' when you want most of the sharpness hidden and wish to retain sharpening on only a small area of your image. (This was a concept that I found confusing when I first began using masks, but I later realized that both are exactly the same mask, but the black one has already been 'pre-painted' for you to hide the entire image, allowing you to 'paint back' with white paint, small portions of your image. Once I grasped the concept, I couldn't believe how simple it actually was.

If you are new to Layer Masks, it is easier to choose the 'Reveal All (White)' Mask, which allows you see exactly what you are 'hiding' (erasing) from the sharpened image.

Once you've grasped the concept of Masks, you will find that they will become one of your favorite Tools in Photoshop and will help you achieve all kinds of wonderful things that could not be accomplished without them.