Distance: 5.6 miles (9 km) round trip
Trailhead Elevation: 4,320 feet (1,315 meters)
Little Nellie Falls Elevation: 4,640 feet (1,415 meters)
Total Elevation Gain: 320 feet (100 meters)
If you're driving to the Little Nellie Falls trailhead from Yosemite Valley or points south, this procedure should see you there successfully:
1) Get yourself onto Highway 140 (listed as "El Portal Road" above). From the view shown here, it proceeds west into the Merced River Canyon past El Portal, climbs out of the canyon to Mariposa, and eventually meets the 99 in Merced. To the east it enters Yosemite Valley.
2) Take the Big Oak Flat Road (120) turnoff from Highway 140 (see a street view of the intersection)
3) Ascend along Big Oak Flat Road, marked in yellow, to the Foresta turnoff (street view).
4) Take the Foresta Road (marked in orange) to this fork in Old Coulterville Road; park here and begin hiking west along the right fork, which skirts the south edge of Big Meadow. The trail is marked in red; the blue hikers marking the trailhead are pointed the wrong way and will never reach the falls, more luck for you.
It's not particularly hard to find the trailhead, but there's a shortage of visual interest to write about in this section of satellite view, so you got to see the directions once again. In case your screen is showing "Devil's Dance Floor" off to the north and this has you intrigued, said dance floor is an expanse of granite with pleasant views but no trail - you'd need to bushwhack from either the Tamarack Flat Campground or the Big Oak Flat Road. The name doesn't refer to interesting geological features; according to Peter Browning's Yosemite Place Names, an excellent source for this sort of arcana, it's named for the impression created when a group of California Conservation Corps workers, no doubt for very good reasons, carried a Model T to this prominence sometime in the 1930s.