I know there are many different ways to apply a tattoo image in photoshop, but here are some quick tips I did for doing a tattoo with the starfish image from last week. Some of this differs a bit for different color and style tattoos, as well as skin tones.
What I did was made three duplicate layers of the image for the tattoo.
Tattoo Layer 1: Set blending mode to Multiply which eliminates the white from the layer and blend with the background layer. Opacity for this layer was lowered to approx 57%.
Tattoo Layer 2: Blending mode set to overlay which helps in bringing some of the color back. Layer set to approx 37%.
Tattoo Layer 3: Layer Fill set to 0% and applied a thin 1 pixel stroke to the layer, then set the layer opacity to approx 65% so the tattoo has a faint black outline.
After doing these layer blending styles, I went back to Tattoo Layer 1 and increased the saturation to somewhere in the +70 range and increased to lightness to the range of +25 to +35.
Areas of the tattoo layers that fell underneath the hand were then masked to hide them.
If you prefer to make the tattoo look like it was recently done, you can always go back and add an outer glow to one of the layers, select a red to pink color, and play with the spread and size until it looks nice and tender. I think multiply mode works well on the glow. Then reduce the opacity of the glow.
To make a tattoo look older just decrease to saturation and add a slight blur to the layers. On curved or angled body parts you can add a mask to the tattoo and lightly mask areas with about 20% opacity soft brush to match the darkness of the tattoo with the highlights on the skin.
I am always playing around and trying to learn new ways, but I thought this presented a fairly decent result in a very short time of just a few minutes.