Reading passages is a long-term skill that depends on your background in English, and like guest 4 suggested reading current literature is the best way to prepare in addition to taking practice tests from gre books.

Here is one strange way of memorizing words if you are having problems. record the word, its meaning and  a sentence using the word on your tape-recorder/ipod/mp3 player whatever you have. whenever you are free, just play it over and over again. trust me the words will be "ingrained" (its one of the 500 gre words by the way) in your memory. its like listening to a song...it worked for me, Hope you will finf it useful.

If you dont have great command over vocabs, and pretty average reading skills by Gre standards, you will need more than 2 hours a day for sure. i would say at least 4 hours. G'luck