Your experiences are pretty close to my first attempts on the white. My advice would be to keep it super simple:
1. Use only one fly, a # 10 olive bead head bugger.
2. Keep moving, do not cast to the same place twice unless you find fish. Make your cast, swing down stream, hesitate at the end of the swing, strip a couple of times, take two steps downstream and repeat.
Like fish anywhere they will go through cycles of being active then less active through the day. During the cooler months (starting about now) mid to late afternoon is pretty reliable.