I found that a combination of things helped me gain sight-reading proficiency. First of all you must love to read through lots of music. I think it was Rosen who said in one of his books that to gain familiarity with many works early on helps you approach them later when you want or need to perfect them. The other thing that helped me was to get involved accompanying--singers, musicals, ballet groups--anything that forces you to continue playing without allowing you to stop and work things out. You quickly learn to anticipate the harmonies, hand configurations ahead of time. Believe me, it really works. It's hard to describe but as you later read through music, your mind begins to anticipate upcoming patterns and your hands are ready for them. Good luck!