First of all, expect to work hard, there is no easy way to learn the language.
To prepare for the Listening Comprehension section (40-60 minutes, 30-50 questions):
* Listen to the native American English speakers: CNN, movies, books on tapes, American radio (you can listen via internet if you have fast connection)
* Use preparation guides:
Cambridge Preparation for the TOEFL Test, KAPLAN TOEFL Workbook
* Find a friend who is interested in improving his English and talk English with him or her.
* Learn idioms and spoken expression, bookstores have quite a lot of books on idioms
* Attend lectures by Americans organized at American Centers.
To prepare for the Grammar section (15-20 minutes, 20-25 questions):
* Do exercises from Grammar books. I would recommend the following books: R. Murphy English Grammar in Use, Cliff's Preparation for TOEFL
* Read books and pay attention to the structure of the sentences. This will greatly enhance your intuitive choice making
To prepare for the Reading section (70-90 minutes, 44-55 questions):
* Read as much as you can. Try to read diverse literature: novels, educational articles, newspapers. Pay closer attention to the educational literature since this is the type of texts you will have on TOEFL. If there are a lot of unknown words in the text, it's ok not to check all of them in the dictionary, try to figure out words from context.
* Learn 5-20 new words everyday. Increasing your vocabulary will improve your score in all sections of the TOEFL. Try to learn recommended word lists from Barron's, Cliff's, Princeton Review or any other TOEFL word list you like. Here is a description of my favorite way to learn words.
To prepare for the Essay (30 minutes, 1 topic):
The only way to prepare for the essay is practice. Of course, you need to repeat grammar rules (which you also need for Grammar section) and punctuation, but without practice this won't give you good essay score. There is a number of ways to practice writing:
* Get the book Barron's How to Prepare for the Computer-Based TOEFL Essay and study it thoroughly (it's really good, I've used it).
* Get a pen-pal, it won't take a lot of time, but it will give you good practice and it's fun.