When shooting in shade, it is possible to get a bright spot of sunlight over a small area of the body (portrait photography). I would like to know the best technique I can use to fix it, and make the brighter area look like the rest of the body (under shade).
The best way to deal with this problem is before the fact. Use an appropriately sized dark panel just off camera to block the offending light to begin with. Noticing things such as light spots in the viewfinder is much easier to deal with than noticing them in photoshop.
After the fact, it is going to be very hard to do and you would need to manually increase the exposure on part of the image and blend the interface between areas together. The correct way to deal with this is to use a fill flash while shooting such that the lighting is corrected to the way you want it to be.
You might also have some luck trying to use curves to bring up the darker parts and bring down the lighter parts, but it may be difficult to get satisfactory results, particularly if you didn't shoot RAW.
I can't help you do it in Photoshop, but it's pretty trivial using Nik Software's Viveza. They offer a trial version; I really recommend the entire bundle as a value considering I would personally have purchased Dfine, Viveza, Silver Efex Pro and Color Efex Pro on their own.
You can also get a trial of the whole bundle.
(As a heads-up, these are not pre-sets like VSCO, they are discrete applications that you hand images off to which may or may not be suitable for your workflow.)