Fake blood (take a look a this tutorial [link] you can also purchase it but it's less expensive to make it and it's basically the same thing), liquid latex, tissue paper and paint.
Basically you use a paint brush to put the liquid latex on whatever area of your body you are working on, then put on crumpled and ripped pieces of tissue. Then paint on more latex and warp it to however you want it to look. (Twisting pieces and applying them can make it make look like veins are popping out, applying pieces of tissue to build up the outside area and then hallowing out the midle can make it look like somethings taken a bite out of you). The paint black, green, blue and purple over certain areas to make it look more like a bruise. Then after you're done all that, paint the fake blood on and you're done
Really nice, but if I could make a suggestion, perhaps use the bruising more sparingly? And maybe add some red into the bruises to make them look fresher
Basically you use a paint brush to put the liquid latex on whatever area of your body you are working on, then put on crumpled and ripped pieces of tissue. Then paint on more latex and warp it to however you want it to look. (Twisting pieces and applying them can make it make look like veins are popping out, applying pieces of tissue to build up the outside area and then hallowing out the midle can make it look like somethings taken a bite out of you). The paint black, green, blue and purple over certain areas to make it look more like a bruise. Then after you're done all that, paint the fake blood on and you're done