Purchase the official GMAT® Exam books.
It is preferable that you buy the latest version.
Do not let yourself tricked into buying other books/materials. If you only study using the official materials you will not hurt your chances of getting 700+ on your GMAT exam.
Reserve 3-4 months for preparing for the GMAT® Exam and then schedule the exam.
Having a set exam date will be a good enough motivation and will help you better manage your time and progress. Being under pressure will allow you to be more focused on getting the big score.
Start by understanding all the types of exercises and then for each type of exercise practice some sample questions.
Start doing the tests from the official materials over and over again.
Keep statistics on the results of each iteration in order to be able to track your progress.
If after going through all the tests for the 4th time you get over 80% right, assuming you will focus during the actual exam, you should be guaranteed a score of 700+ on the GMAT.
A month or so before the exam, after having gone through the official materials start doing sample test from other sources (ex: other books, tests you can find online - due to the very dynamic nature of these materials links will not be provided)
Do not read anything the night before the exam.
... AND MOST IMPORTANTLY
Focus during the exam. Never think you will take it again.
It is your one and only chance to get an excellent score.