As a rule, the writing of the plan of the tour consists of two phases: route development and writing of the text of the tour.
Development of the route is the first you want to start planning trips. If an excursion is scheduled in one place (Palace, Museum, etc.), consider the scheme of movement of the group at this location in accordance with the plan of the building (or area). Sign, when will start the tour, how much time the group will meet near each exhibit just how much the excursion will be on time and what time it will end.

If you plan to tour the city with visits to several attractions, also plan and route a tour bus, producing the optimal scheme of motion taking into account the situation on the roads.
The second stage - writing the text of the tour. In the text there should be no disagreement with the historical facts, so when writing the tour make links to those sources where you get information. After all, if a listener does not agree with you and try to challenge said, you can always tell him where your information and how to check it.

At the same time, remember that the text should not only be informative, but not boring and holding the audience's attention.
When the text of the excursion will be written, and dock it at the time with the route to your story about each exhibit took exactly as much time as the tour group will have to stay near him.