This is a very simple technique, but you have to know when to stop. How the application goes, and how to repair your screw-ups if you've crossed over into finger-painting land. :D
Step 1: Bloody Necessities
Clothes - try to use something you don't wear anymore, to help with NOT buying something new
Scissors - tear and cut and rip as needed
Paintbrush - 2" - dollar store
Hanger if needed
Step 2: Clothing Prep
If I am dressing as a zombie and I have dirty fingers, I just wipe them on my zombie shirt lol. Make cuts, holes, shreds if you'd like. But don't make them look intentional. Rough up the edges by tugging on them, aging them, wrinkle your clothes, etc.
I have 2 bloody shirts in this instructable, one is just fresh blood, the other has some dirt.
I like to take my items out on a hanger and hang them from the tree to work on.
Step 3: Blood Art
To do the same thing but with a single line of blood, use the other end of the brush. If the blood has a single point to LEAVE when being flicked off, you will have a single blood-action on the shirt. This is a great way for laying your effects.
To spray blood onto something, whether it be makeup or clothing, you want to trim the bristles on your brush and run your finger across it. As if to flick the blood off of it, but onto your subject. For best results, make sure your brush has rigid bristles. (Synthetic.)
By this time, if you have been using both sides of the brush, you're messy. So, take that bloody hand of yours and smear it onto your clothing item. This will create the classic "psycho" hand streak, famous for a bloody, stricken victim.
Lastly, to layer your small blood-actions with a bulk of blood, use the bristle-end of the brush, dip in blood, have it LOADED and then place it onto the subject. This will let the blood flow organically, or if you do a very short-distance flick, you will have a big blood spot, which is organic in shape.
Step 4: Careful!
You want to come at the shirt from different angles. This shows more than one situation, you don't want uniformity.
You want to come at the shirt from different DISTANCES. Impact doesn't always occur from the same point. (Blood patterns differ.)
You want to make sure that it doesn't become an art project - exactly. Don't over-think anything.
You want to make sure that you're not covering the ENTIRE piece, you don't want it to look intentional.
You want to make sure to evenly disperse blood, and DIRT, if needed, so you don't have a "clean" item.
You want to VARY your patterns, techniques and LAYER them, so your clothing is convincing.
When it's all said and done, you should have something that is unlike any other.
Tip: if you use too much of one technique, or if you don't like the way a certain part looks, add more blood to cover it up. Use the close-blob technique to distract from it. If needed, layer the blobs to make a bigger action point for covering bigger mistakes. :)
Step 5: Finishing Touch!