Read extensively. This is the best way to prepare for the GRE reading comprehension questions. The GRE usually uses passages from scholarly journals and university presses.
Look over the entire GRE reading comprehension passage first. Do not skip ahead to the questions before reading the passage. Reading the questions first will reduce your ability to focus on the passage.
Make notes on scratch paper as you read a passage. Jot down notes about the writing style, any author bias and intended audience.
Write down the first three words of sentences that contain main points. This will give you reference points within the passage for the questions that will follow.
Refer back to the passage for confirmation when choosing an answer. Do not rely on your memory.
Get in some practice. GRE practice tests and sample questions will present you with samples of the reading comprehension question type.