4. Choose Your Villain Well
Doctor Who villains are as diverse as they are numerous. You get villains that pose a physical and logistical threat like the Daleks, Sontarans or Cybermen. There are also the uncanny, psychologically disturbing ones like the Weeping Angels, Vashta Nerada or the Silence. Then you have the ones somewhere in-between such as the Master, the Great Intelligence or the Ice Warriors. You can also have completely human villains, who raise doubts about the position of mankind in the universe. The villain is there to provide a genuine threat for the characters to solve, and which type works is entirely dependant on the story. There should never be any pressure to reuse old villains for the sake of it, as many of the greatest episodes have created fresh, new antagonists. This is what worked so well in the fan favourite Blink. The episode needed a subtle antagonist that provided a true and fearful threat to innocent people who were beyond the Doctors reach for most of the time. So Steven Moffat crafted one specifically to suit the episodes needs. Thus the Weeping Angels were created, and have since become an iconic Who villain in their own right.