Exercises of all formats are important to practice your language skills, but you cannot go into the TOEFL exam without knowing its format like the back of your hand. Download free practice tests from "Testden" (submitting your email address is mandatory) or purchase the "TOEFL Practice Online" package ($44.95 as of June 2011) from Educational Testing Service's (ETS) official website. "Exam English" offers free exercises for the reading and listening parts of the paper and computer-based test, but does not provide complete practice tests.
Set a strict time limit to complete your TOEFL practice test, in accordance with the limit imposed in real exams. Computer-based practice test applications include a timer, but if you are practicing in the paper format, use an accurate stopwatch -- invigilators won't give you the extra half minute you need on exam day. Furthermore, setting the timer three minutes earlier can give you a few moments to evaluate your answers and spot hastily made mistakes.
Failing the practice test is not disastrous, but shows that you are not ready to take the actual test and you need to study harder. If you have a relaxed approach to practice tests and disregard small mistakes, then you cannot evaluate your true capabilities and determine if you need improvement in certain sections. For this purpose, set a strict goals, trying to surpass the score you aim for on exams day.
Avoid distractions, such as the television, the radio, kids running around the house or the noise of road work from outside, for example. Switch off everything that can get your attention, shut windows and choose a quiet room to practice the TOEFL Test. In addition, do not lie on the bed, sit on the couch or have a snack when taking the test. You won't have such "luxuries" on test day, so sit on an ordinary chair and take your practice tests in real life-like conditions. Also ensure you practice on a QWERTY keyboard, as this is the layout you'll use on the TOEFL exam.