There are many different techniques that can be used by test-takers to study for exams. There is no system that can be singled out and identified as the "best" method of preparation. The learning style of the individual who will be taking the exam is the primary factor that determines the optimal means for learning the material covered on the exam.
By the same token, it is not possible to point to a given process and call it the "worst" method of preparation. I recently saw, however, one approach that has to be a serious contender for the worst conceivable option. On one of the certification forums that I am a regular contributor to, someone posted the following:
"I also would really like to have mock questions and answers or practice tests first to fast track my learning. (Emphasis added)
"It is like a reverse psychology in which you learn backwards-style. You get the answer first so that you can visualize how it is used. Then you read the source of the question and are able to learn it quickly. This style is better than when you read the theory first (which will bore you sometimes) and then the application. For me the application should come first and then the theory becomes more exciting."
My first response on reading the above was a physical shudder and an unvoiced (but very heartfelt) scream. What the poster has described is not a method for learning how to use any given technology (Oracle in this case). The process described above is simply a means of training to answer test questions — and it completely misses the intent of professional certifications.
Preparing for and earning IT certifications is intended to make you more useful to a company that employs people who possess the knowledge areas covered by that credential. Improving your ability to answer multiple-choice questions does not make you more employable. You are not going to see any job postings that have "Must be very good at taking standardized tests" listed as one of the position requirements.
I will grant that, so long as a candidate does not employ brain dumps in implementing this backwards study process, it cannot be considered cheating. That is the only positive thing I can say about studying in reverse. It is a technique that is essentially guaranteed to result in a learning process that has an extremely narrow focus.
The focus when pursuing a certification should be to learn the maximum amount possible, rather than the minimum required. Anything else simply reduces the return on investment of time and money put into earning the credential. You may not be cheating on the exam, but you're certainly cheating yourself.
In any given IT field, there is a considerable body of knowledge that must be learned in order to perform the job well. One of the fields I am most familiar with, of course, is that of an Oracle DBA. People who have worked as Oracle database administrators for a number of years will have memorized thousands of information bits in the form of commands, diagnostic steps, tuning techniques, and recovery processes among other things.
The ideal amount of information an Oracle DBA should know to effectively perform their job is huge. The certification exams created by Oracle University do not even attempt to cover everything an Oracle DBA should know. Instead they have picked a subset of topics that are meant to contain a representative sample of the most critical information a DBA should know. As a result, the exams only cover a fraction of the knowledge that a DBA really needs.
When authors write preparation materials for a given certification exam, they do not try to cover every possible aspect of the topics assigned to the exam. Attempting to do so would result in enormous books that would almost certainly prove to be more confusing than helpful. Instead, authors will try to pick out the most important portions of each topic (or at least the portions most likely to be covered on the exam) and explain them to the reader. The end result is that certification preparation materials cover only a subset of the knowledge covered by the exam.
For the test itself, there are generally around 75 questions on Oracle certification exams. When compared to the thousands of pieces of information a DBA must know to be truly effective, 75 questions disappears into that body of knowledge with barely a trace.
The below diagram illustrates this filtering process. Oracle University does a reasonable job of creating exam questions that ensure a candidate understands a given topic. There is no getting around the fact, however, that the test questions cannot truly be comprehensive given the total body of knowledge that is "covered" by the exam.
What I hope that the diagram makes clear is that the "backwards style" learning process is patently unworkable. There is simply no reasonable argument for starting from the slivers at the bottom and expanding on them to actually gain the knowledge covered by the exam. A person studying using such a method is effectively guaranteed to have major gaps in their knowledge whether or not they earn a passing score.
The best way to get value from IT certifications is to learn the general information on the product or process that is being tested. When a certification candidate has a broad knowledge of the topics being tested, there should be no difficulty answering enough questions about specific aspects of that knowledge base to pass the certification exam.
Starting with the questions themselves will immediately focus the study process on a very narrow subset of the knowledge area covered. Learning the answer to any given question does not provide any insight into other aspects of the same topic. A certification candidate might be able to pass exams with this method but they will be doing themselves a grave disservice when they try to apply their newly certified knowledge in the real world.
If you are serious about earning certifications as part of staring or advancing your career, please avoid this particular shortcut. For that matter, you should avoid trying to take any shortcuts and simply concentrate on taking as much time as you need to really learn the material.