Bloods Honor is mainly played at Glenmoril Caven which is east of Markarth. Inside you have to kill one Glenmoril Witch and take its head. To do that simple search the Glenmoril Witch after it is dead and take its head.

After you have one head you can leave. However, I chose to kill the rest of them. They are powerful, but they are mages. If you strafe their magic attacks they don't do a lot of damage. Going left to right quickly whilst walking towards them will do the trick. Once your blade is in reach of them they will be easy prey.

I found that the easiest way to kill Glenmoril Witches is to sneak and use a bow and arrow. Whenever they are about to find you, retreat around a corner so that you aren't in visual sight of the place that you last dealt damage to the Glenmoril Witch from and they will never find you. If you are having trouble locating the witches I found that the map is very useful as all the side caves in which the witches can be found branch off the main cave which will be visible on the map once you are in the main cave.