One of the most common things you'll deal with when it comes to portrait subjects is red skin. This super quick tutorial will show you a fast and effective way to get rid of it in Photoshop.
Coming to you from Unmesh Dinda of PiXimperfect, this great tutorial shows you how to quickly remove red skin using Photoshop using a hue/saturation adjustment. When you're selecting the red color, make sure the size of your selection area is bigger than point sample (such as 3 by 3 average), as this will give you a much more accurate result. Also, be very careful when making the adjustment, as your first instinct might be to simply decrease the saturation of the reds, but this typically leads to a rather unnatural result and can introduce strange gray spots on the skin. Notice how Dinda mostly uses the hue and lightness sliders to achieve the effect. Also, don't worry too much about being ultra-precise where you mask it in; just grab a soft brush, and as long as you avoid any areas that are red and that shouldn't be changed (like hair), broad strokes over the general area will do just fine.