Establish a plan and a preparation timeline

The absolute first thing is to allocate enough time to study. If you have 1 week to prepare, you may pass, but in no way you will get scores that will look stellar. Make a good plan and schedule your study sessions. Monitor your performance by evaluating your practice test scores.

Do some research and get the best study materials and stick to it

Do some research and find the best materials that fit your learning needs. Do not buy all books that are out there. Focus on the very best ones, usually by choosing from the first 3 top-ranked resources from talking to friends and surfing on the Internet. Check my selection of books here.
Buy one or two of those good books and read it more than once. I believe you retain more information if you read the same material more than once as opposed to reading it once and slowly.

Practice with tests as much as possible

For the TOEFL, what matters are not only how much you know, but also how well you can apply this in practice. They want you to be able to communicate in different environments. Split your time, about 50% tests and 50% textbook reading.

Control your anxiety and keep a positive attitude

For many of us it is difficult to manage that amount of information at once. Let me break the news: it is only going to get worse, more information will come, and faster. But do not worry: odds are that you will succeed. So do your best and be confident that you will pass. Positive attitude is a big ally.

Respect your limits

It is not useful to study when you are tired. So try to establish a decent schedule so that your brain is actually working when you are in front of a book.