وعليكم السلام.. I think the most useful thing before taking the test is taking the practice test offered on the TOEFL website. It resembles the real test and gives you the same time limits and then you get a total score at the end of that test. It coasts about 29$. I don't really remember. As for a useful book, I would recommend Barron's TOEFL ibt. I wish you the best of luck
