I had a TOEFL course in a Language Center and I used the Longman TOEFL iBT Prep Book. I remembered that the only person that has the answers of the Pre-Test printed in the book was the Teacher and, because of that, we did those Pre-Test in class. At home, I practiced with the Longman CD, I can get the answers and review my mistakes in each Section.
So, if you do not have the Longman Teacher Book, I think that it would be better for you to read the Skills that appear in the book and then practice with the CD. There are about 8 Mini-Test and 2 Complete Tests.