Hello,

You need to give the IELTS/TOEFL along with the GMAT exam. These are the only exams you need to prepare for.

1. Start your GMAT exam process at least six months before your test results are due. Most test takers report a minimum eight-week study timeline is ideal if you are somewhat familiar with the underlying GMAT exam content. But, you can study however you want and focus on what topics need your attention first and move on accordingly.
2. Review and study one section of the test at a time.
3. Review basic math skills.
4. Practice pacing, because time management is critical to completing the GMAT exam.
5. Review the types of questions in the Analytical Writing Assessment, Integrated Reasoning, Verbal, and Quantitative Reasoning sections  .
6. Use the free GMAT™ Official Practice Starter Kit and Exams 1 & 2 to help you become familiar with the format used.
7. Expand your preparation with more questions by using GMAT™ Official Practice Exams 3, 4, 5 & 6  .
8. Practice with real GMAT questions, answers, and explanations using the GMAT™ Official Guide  .
9. Review the GMAT™ Official Guide Verbal Review  or the GMAT™ Official Guide Quantitative Review.
10. In the end, review all that you have studied, notes, revise all the topics for equal amounts of time.

Hope this helps!