Yosemite being my all-time favorite, I recommend doing the Vernal Fall hike, unless you are willing and able to do Half Dome. Another good day hike is the Mirror Lake loop. Strenuous is the Yosemite Falls hike, very uphill.
Aside from those, each good for a day each, visiting Glacier Point, Toulomne meadows, driving to Tioga Pass are all good for a day each. Using the shuttle all around the valley is a good day. See the Ahwahnee Hotel and also the museums.
This only scratches the surface. If you want more hiking, fishing or back country camping, you could spend a lifetime.
Enjoy.
P.S. I like Upper Pines best. YMMV.
This only scratches the surface.
