If you have more than one day to spend in Yosemite Valley, use the first day to get acquainted with where everything is in the valley. This will also give you time to acclimate to being almost a mile in the sky. If the shuttle is running, take it around the valley and get off at each stop to see what is there and how the views of the waterfalls and mountains have changed. Visit Happy Isles and walk over to Mirror Lake/Meadow, visit the Indian Village and the Native Center, see the natural history displays at the Visitors Center, and watch whatever video is showing in the theater behind the center. Walk through the meadows, visit the cemetery for its historical occupants, and watch rock climbers make their way up El Capitan or the Royal Arches. Have afternoon coffee or ice cream on the outdoor patio at Degnan’s. It has a good view of the Lost Arrow and there might be climbers doing a Tyrolean Traverse to it.
On the second day, take a hike up to Vernal and Nevada Fall and have lunch overlooking Nevada. If you feel you’re in pretty good shape, continue beyond Nevada Falls to Glacier Point on the Panorama Trail (crossing the top of Illilouette Fall), and come back down into the valley on the Four Mile Trail. Have dinner at the Ahwahnee Hotel.
If you have three days, hike up to the top of Yosemite Falls. Now you have a choice. You can either head left for the top of El Capitan and return this way, or head right for North Dome, Indian Arch, and Snow Creek Fall, coming back down into the valley in Tenaya Canyon with its unmatched view across its valley of Half Dome.
With four days you can hike up to Half Dome. If you have five days, hike up to Glacier Point on the 4 Mile Trail and take the Pohono Trail to Inspiration Point, seeing Sentinel Dome, Taft Point, the Fissures, and Dewey Point along the way. With six days, build in a day to let your body recover, or hike around on the trails in the west end of the valley.
And if you have a full week to immerse yourself in the glories of the valley, hike up to Clouds Rest.
If you don't want to do any hiking, simply wander around the valley, sit in scenic places, and watch and listen to the valley go about its daily life. As the sun moves over the mountains, all the granite features change their appearances. Day trips to Tuolumne Meadows, Mono Lake, and the Mariposa Grove of Giant Sequoias are also well worth the effort.
Whatever time you have, if you can be in a meadow for sunrise and sunset, and again at night to watch the stars, you will count yourself blessed. Even the scent of the pine-scented air is enough to knock you off your feet.