Frequency Separation is a really great way to touch up skin and other areas, and one of my favourite go-to techniques. It works by separating the colour and the texture onto different layers, allowing you to edit them independently of each other for maximum effect. It's really quick to do, but can take a little bit of practise to master fully - but it is so worth it, I've found it to be the best way to touch-up skin; far better than spot-healing tools used in isolation.
A great way to make this even easier is to automate the process by recording it as an Action. I'll likely be doing a full tutorial on how to do this in the future, but if you already know how to do it, this is a great way to turn a dozen clicks into one! I also set Gaussian Blur to a custom command so I can do it with a keyboard shortcut instead of having to go to Filter -> Blur every time. Whenever there is a process you go through a lot, I recommend creating a keyboard shortcut for them! You can alter these by going to Edit -> Keyboard Shortcuts. Actions and Keyboard shortcuts are a great way to make editing more efficient and streamlined!
Step 1 - Create the Layers
Duplicate the layer you intend to be editing twice. You can do this with CMD+J on a Mac! Name the first layer Colour and the second one Texture. the Texture layer should be above the Colour layer, so move it if necessary. For organisation, I group these layers into a Folder which can be named Frequency Separation
Step 2 - The Colour Layer
Hide the Texture layer by clicking the eye icon, and then select the colour layer. Go to Filter -> Blur -> Gaussian Blur, and blur the layer so that the image is lacking in detail.
Step 3 - The Texture Layer
Make the texture layer visible again and select it. Go to Image -> Apply Image, and a little dialogue box will pop up. In the Layer section, select the "Colour" Layer, and set Blending to Subtract. Click ok. Then set the Texture Layers blending mode to Linear Light.
Step 4 - Touching up the Colours
On the colour layer, using the lasso tool, select areas of a similar light and colour, and apply Gaussian Blur as before - adjust the settings to suit the image. You can select large areas for generic touch ups, or focus in on individual blemishes to touch up the specific region.
Step 4 - Removing Blemishes
Now select the Texture layer, and pick the Clone Stamp Tool. While pressing alt click on a part of the image near to the blemish you intend to remove to create a sample. This area should be free of blemishes, as the tool will be replicating this are. Now, with the Clone Stamp Tool, paint over the blemish until it is removed. You can repeat this process for all the blemishes you wish to remove. I recommend resampling the tool regularly for the best results.
Take time to perfect the technique, if you push it far it can create a very "airbrushed" look. If you want something more natural, go easier on the Gaussian Blur and be selective over which blemishes to remove.
Hope you find this tutorial helpful! Be sure to check out more for additional advice!