To show that this should work on any skin texture, I'm using one I randomly pulled from the internet, shown here:

Spoiler:

For some reason, I've seldom seen tattoos done correctly. Tattoos are ink; they're supposed to look like they've been inked into human skin. It's even worse when the modder has tattoos of his own and doesn't even use them as reference! Then the tattoo ends up looking something like this:

Spoiler:

That looks like a sticker, not a tattoo. Even if you drop the opacity, it still won't look right. It'll look dull, washed out and gray. You need to use Photoshop's Blending Options to get a more accurate looking tattoo. Look at some reference photos of people with tattoos. They shouldn't have 100% opacity... but shouldn't look ghostly or too washed out either.

Spoiler:

Tattoo Layer Order:
Multiply (30-50% opacity, depends on the ink quality)
Soft Light (70% opacity)
Color (30% opacity)

Here are our end results:

Spoiler:

Very useful tutorial! Thank you man!

Thanks dude, hope it's simple enough for anyone coming through here, I tried to go pretty "step by step" with it.