Exam 70-668 has a reputation for being brutal, so you are going to need all of the help that you can get. The first bit of advice that I would give you is to be careful about the study resources that you use. There are a lot of “brain dump” sites out there that claim to provide real test questions and answers, but these sites are quite dubious. Many of the sites are filled with inaccurate information, and there are even some unconfirmed rumors circulating that Microsoft has set up some fake brain dump sites (which require a free registration) as a way of catching test cheats.
Even though I recommend staying away from brain dump sites, I recommend looking around on the Internet for practice exams. This is important even if you already know SharePoint inside and out. The reason I recommend practice exams is because the types of questions that you will encounter on this exam are very different from what you would encounter on a lower-level Microsoft exam. Regurgitating material that you learned from a book isn’t enough. You have to think like a consultant who is trying to solve tough business problems. Finding some practice exams will help you to get a feel for the types of questions that you will encounter on the exam and the thought process that you will need to use to correctly answering those questions.