Ill start off by saying that the better the pic of the tattoo reference the better the tattoo will come out. So ill start off with this pic of Sean Mays Tattoo:

Crop out a little piece of the tattoo to be easier for you to make and create a new layer:

Then zoom in to where you best can make it:

Then grab the pen tool and start drawing the tattoo and then go to paths and hold Ctrl and click on where it says work path and it will be selected.

Then go to Edit - Stroke - and use these settings:

Then click ok and deselect by holding Ctrl and pressing D or going to Select - Deselect. Then youll get something like i have below:

Now you see how theres some black inside of the tattoo selection we made. To color that use the pen tool and select the black inside part of the tattoo selection and then go to Edit - Fill and use these settings:

Then use the pen tool and finish the tattoo and keep on doing the same thing and youll get something like this:

When you're finished go to File - New - and use these settings:

Now drag the layer where you made the tattoo on to the new document you just made and free-transform it until it looks similar to this:

Now your done. Tto put the tattoo to a skin file drag the tattoo layer to the skin picture and set the tattoo layer to multiply and you're done:

*Thanks to Kuttan for teaching me kinda how to make tattoos*