1. Make The End Memorable
Just as the beginning of an episode is what ropes us in, the end is what we will remember. Therefore, the last few minutes before that iconic theme whistles out are crucial. My personal champion example of this is Utopia. This episode brought a beautifully executed plot twist in the last ten minutes, leaving the audience with a cliff-hanger without no clue to an obvious resolution. I still remember it five years later. It usually works if the narrative is not entirely resolved. It doesnt even need to lead to a continuation. I specifically refer to Blink. The story is resolved and theres kind of a happy ending, but it concludes with the allusion that the Weeping Angels are everywhere, and the Doctor wishes us good luck against them. Of course there is also the choice to make the end a particularly emotional moment. Any of Paul Cornells episodes fit this bill. But however its done, the end of the episode should stick with the audience for a long time. OK, now thats the dos out of the way. Now onto the donts of writing Doctor Who.