Listening Section - Listening for intonation is very important. A rising tone often indicates a question, and a falling tone often indicated agreement.
Structure Section - Go back to the practice tests after you take them, and study the words you thought were difficult.
Reading Section - Read as much material as possible, including books, magazines, and newspapers, to increase your knowledge of the structure of English.
Writing section and TWE - Be sure to support and explain any general statement you make with facts, specific details, or reasons. Also use clear transition words, such as in general, for example, or as a result, to enhance your writing.
TOEFL test prep resources:
TOEFL.org - the official TOEFL web site
GetTOEFL.com - TOEFL reading skills and practice tests
Computer Based TOEFL practice test