The best way to see Zion is to spend a week in the park, starting with the visitor center displays and programs, then taking a Zion Canyon Scenic Drive trip on the shuttle bus, and gradually working from short hikes and walks to full-day and overnight treks into the backcountry. That's the ideal; but for most visitors, time and finances dictate a shorter visit.
If you have only a day or two, we recommend that your first stop be the Zion Canyon Visitor Center near the south entrance to the park, to see the exhibits, look through the free Zion Map & Guide, which describes various hiking and viewing options, and finally talk with a ranger about the amount of time you have, your abilities, and your interests. Because Zion has such a variety of landscapes and activities, each visitor can easily create his or her own itinerary tailored to his or her own interests.
If your goal is to see as much of the park as possible in 1 full day, we suggest the following:
After a quick stop at the visitor center, hop on the shuttle bus, which hits the major Zion Canyon roadside viewpoints, plus the new Zion Human History Museum. When you get to the Temple of Sinawava, instead of just taking a quick look and jumping on the next shuttle, hike the easy 2-mile round-trip Riverside Walk, which follows the Virgin River through a narrow canyon past hanging gardens. Then continue the shuttle bus trek back to the lodge (total time: 2-4 hr.), where you might stop at the gift shop and possibly have lunch in the lodge restaurant.
Near the lodge, you'll find the trail head for the Emerald Pools. Especially pleasant on hot days, this easy walk through a forest of oak, maple, fir, and cottonwood trees leads to a waterfall, hanging garden, and the shimmering lower pool of the Emerald Pools. This part of the walk should take about an hour round-trip; those with a bit more ambition may want to add another hour and another mile to the loop by taking the moderately strenuous hike on a rocky, steeper trail to the upper pool.
If you still have time and energy, drive back toward the south park entrance and stop at Watchman Trail Head. Here, a moderately strenuous, 2-mile, 2-hour round-trip hike takes you to a plateau with beautiful views of several rock formations and the town of Springdale. That evening, try to take in the campground amphitheater program.