Maybe ready your hand position. I was in your shoes once but I still also need practice. just practice everyday. remember, the examiner might give you 30sec-1 minute to examine the piece. in that time, try to play it on your laps. hope this helps.
I can't give any real help as I'm still not that high level.. but secretly speaking i feel some video games may help improve the certain abilities you need for sight reading ^o^
I'm an amateur, but took 3 years of lessons from a top piano professor at my university. One of the best things he left me with was a solid foundation for sight reading. He had me do exercises from this book.And, during a lesson, he pushed and pushed and pushed for me to keep my eyes on the page for a piece I was learning.If you combine that book with a teacher who knows how to coach for sight reading, you can definitely learn it. And, I'm certainly not a great sight reader yet, but for most fairly easy pieces I can sight read them with 80-90% accuracy, and I can read more advanced pieces comfortably enough that it is not agonizing. Which means, as an amateur, I can read music like I'm reading a book and just enjoy it instead of painstakingly decode it. One important thing for sight reading is keyboard orientation. That book has exercises that are only about finding the groups of 3 and groups of 2 accidentals with your fingers instead of your eyes. It really helps!Another important thing is learning to read intervals and phrases rather than decoding individual notes. This book will help you to learn that as well. It also breaks it into pieces, some exercises are just for pitches, some are for rhythms that you just tap out. It really works! Good luck.
Topic: Hopeless sightreading 