Essentially:
1. You will need some kind of pet/minion or something that can fight for without prompting.
This can be a hunter pet, warlock minion, a pet or other guardian that is given to you for a
specific quest or game feature.
2. You will need to find a location where an NPC mob can be killed easily by your pet/guardian.
3. The NPC must re-spawn frequently.
More examples and detail in the video: