First you are going to paint your nails with two coats of a white polish. I chose to use Essie Blanc. Then you are going to to want to top coat this so that when you add red they don't bleed together to turn into an awful strawberry milk color. Don't really worry too much about cleanup because it is about to get really messy!
Next you are going to add blood spatter! There are lots of different methods and tutorials but this is just how I do it. Take your bottle of polish, for this I used Zoya Rekha, remove the cap and put it to the side. Now you are going to take a drinking straw and dip it right into the bottle of polish. You do not need to stick the straw all the way to the bottom just stick it in far enough for the tip of the straw to become covered. Quickly aim the straw at your finger and blow through the straw with one big breath. As as much or as little "blood spatter" as you like. This can get very messy so clean up your skin and around your cuticles as you let the spatter dry before you add top coat for the next step.
Now you could stop here or continue on to the next step to take the creepy up to another level. I thought it would be cool to have a little note on my nails in the classic serial killer type ransom letter style with cut out letters from a magazine. For this you will need to work one nail at a time. Add a layer of top coat to your nail and then add your letter clipping to your nail and position it. If it keeps peeling up push it down and hold it in place for a few seconds. Also as the top coat dries it will be easier to push it into the topcoat and make it stick. Once you have it successfully pushed down add another layer of topcoat to seal it all in. You should end up with something creepy like this!