Tattoos are a completely different beast when it comes to retouching and post process in Lightroom. Using global edits will affect the entire image and will have some negative affects on skin, hair and anything else in the scene. This tutorial will walk you through building an adjustment brush to make tattoo's pop of the page like in our example above.
This technique will work for all types of tattoo's wether they're black and white or full of color. There's a more involved yet powerful technique I use in Photoshop, but this quick and simple adjustment brush should be enough for most images you have.