When I have skittish fish, I'll bring a chair over next to the tank and try to sit there for an hour or so each day (usually reading, sometimes watching TV). I think it gets them accustom to me and maybe helps them associate me with food (and therefore a good thing) or at the very least that Im not a threat. Its a slow process though. It seems like it takes 3-4 weeks of this before I see improvement.
I doesn't always work though. My Ember Tetras and Pygmy Corys never seemed to get used to me this way. Adding more made a big difference in my Embers, but the Pygmies still dive for cover whenever I walk by.