I decided to make this to help other's with their costume. This was the first time I did this, so it's not perfect.

What you need:
Liquid Latex,
Q-Tips,
Sponge,
Toilet Paper,
Scab Blood,
Gel Blood,
Gloves (optional).

I got all of my items, except the q-tips, toilet paper and gloves from a local Halloween store. Any Halloween store will carry it. The name of mine was Halloween Spirit.

Step 1:

I started by putting a base coat of liquid latex around the area of where the wound would be.
I used a sponge to get an even layer, I let it dry, and then did 1 or 2 more layers until I was satisfied.

Items Needed In This Step:
Liquid Latex,
Sponge.

Step 2:

I then proceded to use the liquid latex and made a smaller area of where the wound would be, so it would rise a little. As you can see, it pooled to the bottom, so I had my head tilted while it dried.

Items Needed In This Step:
Liquid Latex,
Q-Tip,
Sponge.

Step 3:

While doing this, I made the mistake of squeezing my sponge, therefore ruining it, so don't do that even to clean it off. It will stick together and be useless. Lucky for me, the bottom of it was still usable.

Step 4:

I then took 1 sheet of toilet paper, ripped it in half and rolled it. I got 2 the size about of where I want the wound to be.

Items Needed In This Step:
Toilet paper.

Step 5:

I then formed it into where the wound would be. I used the Liquid Latex to hold it down. (or use molding wax, this would be easier).

Items Needed In This Step:
Toilet paper.
Liquid Latex,

Step 6:

After that, I tried smoothing it down a little, so it wasn't raised a lot. I put liquid latex over it to hold it down, then i rubbed my fingers over it to hold down, and to tear the toilet paper a little to make it uneven.

Items Needed In This Step:
Liquid Latex,
Sponge,
Q-Tips.

Step 7:

After it dries a little, I took my scab blood, which looks like this.

Step 8:

It's thick and messy, so that's why I was wearing gloves in the first place. It didn't stain my arm when it got on it, and it peels off pretty well. Before I put it in the wound, I did a last layer of liquid latex around the edges, it doesn't need to be dry, because it mixes with the blood.

Items Needed In This Step:
Liquid Latex,
Scab Blood.

Step 9:

I then rubbed it around to get that bulged, fresh wound look. The main of the goop was inside the wound, and I just smeared it around the edges, to cover all of where I put the liquid latex. The latex I used dries clear, so if it get's on your face, that's fine.

Items Needed In This Step:
Scab Blood,
Q-Tip.

Step 10:

I then took my gel blood, and did as I was told to melt it.

Items Needed In This Step:
Gel Blood.

Step 11:

I then put more inside the wound and a little smearing outside, so when it dries, the different colors would combined.

Items Needed In This Step:
Gel Blood.

Step 12:

This is the final result that I got. I didn't leave the blood to drie, since I was just taking it off, but this is how it should look.

Step 13:

And I just tore it off, and I can save it for later. The only thing I got on my face was a little of the scab blood, which I rolled right off.

Hope this helps and you enjoy it!