I'm not a terrible sight reader or anything, but it always helps me to hear the song first. I know that is cheating, but I am an auditory learner, and once I hear something I can play it almost perfectly from that point on.

Helps when I screw up on Guitar Hero, as well. My friend will sing 2 bars of my part when I screw up/get lost and then I am fine for the rest of the song.