It's important to be on time to meet your guide; check the details of your reservation because s/he may have to pick up others after you.
Our guide was knowledgeable and energetic, and gave us so much more than the simple description of the tour! As we drove through Paris to pick up other members of the group, she gave a constant running commentary about the sights we passed, in spite of the challenges of traffic along the way. My father and I were very glad of the opportunity to visit sites on the grounds of the Versailles palace that would have required considerable time walking, that our guide was able to drive us to in our shared van. On the way to Versailles, we went efficiently via highways, but on the way back, our guide chose a route that allowed us all to enjoy some beautiful close-in suburbs of Paris, and magnificent views of the city.
Versailles is a complicated site that demands repeated visits, but this tour was an excellent introduction, with easy transportation to and from the site and superb commentary from our guide.