A preparatory student often faces the situation of choosing Toefl/IELTS or GRE/GMAT to attempt first. To me, this often is a simple personal choice based on the student’s confidence levels. However, tentative students may want to attempt Toefl/IELTS first. I say this because, Toefl/IELTS is less taxing than GRE or GMAT. It also lays the foundation for preparing for these aptitude exams (GRE/GMAT).
Language requirement tests (Toefl/IELTS) can get you started and give you confidence. One has to understand that there are different set of parameters that these tests focus on. With language, you will have to demonstrate that you can communicate well (both orally and written). With aptitude, it is different. Analytical thinking, math, and logical reasoning are tested. Of course, to do well, you must be proficient in English. It is obvious that the better you understand a question, the better you answer it.
Preparation for these exams must start very early. In my opinion, students can start as early as 2 years from graduation (BS degree). This gives the time for multiple attempts, thorough preparation and self confidence. While studying and practicing is important, the best way to boost one’s confidence and test their performance is by taking mock tests. There are several that are available by various vendors such as Kaplan etc.