Here is a Kat Von D look I did a few years ago. I just copied her typical makeup look (albeit with a heavy hand) and covered my arms with temporary tattoos found at a dollar store.
I won't go through the basic makeup as this photo is several years old and I can't exactly remember all the products I used, but I will show you how to recreate the star tattoos she has on her cheekbones and temples. Apply your star tattoos after you have completed the basic makeup.
First draw 1 - 2 stars on an approximately 1" x 1" piece of masking or green painters tape (you won't want to use clear tape as it can rip easily.) Using an Exacto knife and a cutting mat, carefully cut out your drawing, and peel it away using the tip of the Exacto knife.
Then stick the tape to your skin, and with a small brush, apply a medium thick layer of MAC Blacktrack Fluid line to the stencil, making sure to work the product into the corners of the stencil, overlapping slightly onto the tape to ensure you get crisp edges. Allow the liner to dry for at least 30 seconds then slowly peel the tape away and repeat.
To make the tattoos seem even more convincing, once you are finished applying them, lightly brush them over with setting powder and highlighter. Having a thin layer of makeup on top of them will make them look as if they are truly part of your skin!
What is your Halloween costume this year?