There are two major areas of ruins in Mesa Verde National Park. The largest and most-frequently-visited is Chapin Mesa. Any visit to the park typically includes at least one trip around the two loops on Chapin Mesa: Cliff Palace Loop and Mesa Top Loop. Managing priorities and time in Chapin Mesa can be a bit challenging, but one suggestion would be the following if a whole day can be spent there:
If possible, book a twilight or photography tour (on Recration.gov) of Cliff Palace and a morning tour of Balcony House (tickets at the visitor center and Morefield Ranger Station two days in advance). Alternatively, book the regular 1-hour tours of Cliff Palace in the morning and Balcony House tour in the late afternoon. Tour tickets in hand, take the morning tour before you head over to the Mesa Top Loop to view the mesa-top dwellings, the Sun Temple, and the great overlooks on the loop. Head back to the museum to spend some time watching the film, touring the exhibits, eating lunch at the restaurant or the picnic area, and touring Spruce Tree House on your own. In the afternoon head back over to the Cliff Palace loop for the afternoon tour and, if there is time before or after, the short hike out to the Soda Canyon Overlooks.
If there is more time, another day can be spent on Chapin Mesa by doing the Petroglyph Point Trail and spending some time wandering through the Far View site and visiting Cedar Tree Tower. The drive back down to the Morefield Campground or out of the park altogether is very beautiful at dusk, and there are several scenic overlooks to choose from on the trip.