Teaching TOEFL can be a complicated task. I find there are two main things to do when teaching TOEFL preparation.
1. Find a good book
2. Break it down into smaller tasks
1. Find a good Book
I think is is important to have a good preparation textbook when teaching TOEFL. The first reason, is because these books show an authority on the test that photocopies, Internet printouts, and other resources simply can't provide. Ideally the student will purchase a copy of the text and work along with your copy. This way the student can use the exercises and supplementary material at home.
My personal favourite book for the IBT test is Cambridge TOEFL Preparation. This book has the most detailed explanations of the grammar points that are covered on the test. I highly recommend this book.
2. Break it down
Don't just start giving practice test after practice test. Break it down and make it clear to the student all the areas of English that need to be improved in order to do well on the test. Explain that grammar, reading, writing, listening, pronunciation, and vocabulary are all important. More than that, explain how each topic is tested, and what each topic contains. For example, it is important to show all the necessary grammar points that are used.
Guide the student along with a study plan, that covers all the areas listed above. Allow for time to practice each area, and focus on those skills that are weakest.