For example, instead of seeing this:
as a C and an A (in treble clef), I see it as a sixth, with a C as the lower note.I knew from the start that that would help, but today found that an "I am NOT going to look at the individual notes!" attitude is helpful.
I'm finding that one key to making sight-reading work, is to have the music trigger movement of my hands rather than result in some kind of intellectual process. As soon as the interval is recognized as a sixth, my hand automatically adjusts itself to the shape needed to play a sixth.