Hi!!
there have been a lot of discussions on sight reading, and really the only way to improve is to play anything and everything!!!just pick up a piece of music u have lying around that you havent played before and play it!!in the exam make sure you check the key sig, time sig and any speed markings. also look for any accidentals in the piece or tricky parts. in the 30 secs you get always try the ending for a good finish!
basically i would say there is only 1 way and that is to play and play!!! i did and now although i dont like sight reading i have got a lot better!
hope this helps
Nat