I'm assuming you are referring to "Porcupine Creek" (a/k/a the North Dome trailhead, since that's what most people use it for) as opposed to "Porcupine Flat" (from where you could follow the Old Tioga Road to either the Yosemite Creek or Porcupine Creek trail, but note that despite what the maps may show, this "trail" isn't maintained.)
From Porcupine Creek... even if there is not much snowpack, you may have a few unbridged creek crossings that could be tricky depending on runoff: one right at the beginning at Porcupine Creek (look for a log upstream--it's been there forever), then Lehamite and Indian Canyon Creeks, both of which are between North Dome and Yosemite Creek. If there is going to be snow, you'll hit it early--mostly between Porcupine Creek and the first trail junction. You can bypass Lehamite by taking an alternate trail from this junction, but North Dome is one of the highlights of this route. Be sure also to stop at Yosemite Point and to go out to the overlook above Yosemite Falls.
The trail is mostly in fairly open forest except for the stretch between Indian Rock Arch and North Dome and the area between Yosemite Point and the valley floor. From the trailhead it's mostly downhill, and the only really steep part is the drop into the valley below Yosemite Falls.
