Because you'll be taking an exam under rigid time constraints, it will be important to strategically manage your time -- even during practice sessions. Although the revised GRE that debuted on Aug. 1, 2011, allows you to go back and review your answers within a section, you'll need to make sure you leave yourself enough time to complete all the questions within each section.
One important consideration for managing your time is that it's important to have extra focus on the early questions of the math and verbal sections. If you answer these early questions correctly, the computer-adaptive testing system will provide you with more high-value questions, which will help you achieve a higher score. If you get them wrong, however, you'll be stuck with lower-scoring questions. For the first 10 or so questions, move slowly and double- or triple-check your answers. However, you should always keep an eye on the clock, making sure you have enough time to finish.
Don't waste your time trying to guess whether the questions on the exam are getting harder or easier. Moving deliberately through the exam will help increase your score; trying to get into the computer's head will not.