I recently finished five out of ten of the Nobz I am painting for Shaun Kemp's ETC army. I'm really pleased with how the blood came out on the mad dok.
Blood is a very difficult effect to achieve with model painting. It is very easy to go overboard and make it look terrible. My method is pretty simple, and I am very happy with the effects. I remember there was a picture of an Eversor Assassin in the Assassins codex back in 3rd ed. The blood on his blade was so well done, and I have tried to emulate that with this technique.
Step 1: Scab red. Think about how the blade would have gotten blood on it. if its a sword, paint streaks of red parallel to the motion it takes when it is being used. If it is a bandage of a wound, blot the red on.
Step 2: Blood red. Blood dries from the outside in, so keep the edges of the blood area scab red, and use blood red to bring out the center of any blood stain.
Step 3: Gloss Coat. This is a really important step. dab on some Gloss Coat on to your blood mark. It will make a huge difference.
This is a quick but very effective method to get a good blood effect. Remember to err on the side of less is more with blood effects.