Directors or Game Masters?
This is the basic formula of every episode of Doctor Who. Use it as the template for your scenarios, or as a frame of reference if you decide to digress from the formula.
The Time Lord and his companions land the TARDIS someplace new and begin to explore, soaking in the unique features of the area. In the midst of exploring, the TARDIS crew discovers a conflict or problem that puts them and the inhabitants of the setting in danger. The TARDIS crew endures peril while facing overwhelming odds and powerful foes. In the end, they use their intelligence and imagination to resolve the conflict or problem, but not without facing one last, climactic danger. As a result of facing the danger and resolving it, the crew comes to a greater understanding of the mysteries of the universe, the history of the world, and/or of themselves and their place in it. They then return to the TARDIS to travel to a new location to explore and start the whole cycle over again.