Use the available test aids. The makers of the test offer a number of test-preparation materials, both for purchase and for free. See TOEFL study materials for a list of test materials for the online version of the test. The makers even include value packs that combine a number of the materials in one set. At the bottom of the page, they offer some free resources. You may also be able to find study materials in your local bookstore.
Study over time. Cramming works sometimes, but rarely does the information survive taking the test. Your TOEFL scores are only good for two years after the initial test because your abilities can change over that period, making the previous score invalid. Thus you want to study so as to retain the information over the long term.
Interact with English speakers. While practicing alone or with the computer is good, there is nothing quite like actually holding a conversation with another person, especially a native speaker. Consider it a form of practice to go out and hold a conversation in English with at least one person a day. This will help with the comprehension portion of the test where you must listen.
Write a little every day. Writing is a necessity of the test; therefore, you should practice by writing at least one paragraph a day. One way to do this is to find a website offering both your native language and English, choosing a paragraph, translating it into English yourself, and then comparing it with how the website presents it in English. Try to be as accurate as you can be in your translation, especially in the placement of words. ETS suggests keeping a daily journal of your activities.
Use a standard English keyboard. A QWERTY computer keyboard is what is used in English-speaking countries. Familiarizing yourself with it will help you be comfortable with it come test time.