Each person who is preparing for tests has to decide the best approach that works for him by considering his learning style as well as general lifestyle.

Self-Learner: 
Such people prefer to learn material at their own pace by reading the books themselves on their own time. They are usually very self-motivated and can find time to study on their own. These people can usually prepare for a test by buying books, reading information about the test format, and taking practice tests on their own.

Visual Learner: 
Such people usually understand material much better if they are shown practical applications or generally shown how to solve problems. They can prepare for the tests by buying video and audio test preparation lessons to learn the concepts at their own pace and then practice the problems by buying workbooks.

Learn from a Teacher 
Such people usually understand the concepts best if someone explains the underlying fundamentals clearly to them and then these people can learn and add on to this knowledge on their own. They benefit by taking tutoring lessons (if possible, one-on-one) by an expert tutor to clarify any doubts and understand the basic concepts. These people can then practice the problems by working through workbooks and discussing difficult questions with their tutors. 

Choose your approach for test preparation, whatever your learning style is. Of course, a tutor can definitely help you understand difficult concepts, but you will still need test preparation books to get enough practice so that you feel confident for your exam. If you have the confidence, you will most likely be able to break the problem in manageable parts in the test and relate it to some problems that you had practiced earlier.