Reading comprehension will seem difficult at first, but like most things in life, with practice, it’ll get easier–much easier. Practice reading GRE-level materials, like The New York Times or The Wall Street Journal, on a regular basis. Articles from The Journal and The Times are of the same caliber as the GRE, and since it’s daily, your reading source will be endless. Make sure you get the online version so you’ll get used to reading long articles from a computer screen (since the GRE is strictly a computer adaptive test except in a few select regions).
BrE caliber AmE /ˈkælɪbə US -ər/ n
the level of quality or ability that someone or something has achieved
of sb’s calibre
Where will we find another man of his calibre?
The school has always attracted a high calibre of student.
of high/the right etc calibre
The paintings were of the highest caliber.
of this/that calibre
The city needs a hotel of this calibre (=of this high standard) .
[C] a) the width of the inside of a gun or tube
a .22 caliber weapon
b) the width of a bullet