Have you checked whether you will be required to take the TOEFL or a similar test of English as a foreign language? (If you did not do your university education in English, then there's a good chance the schools will require you to take the TOEFL, IELTS, or a similar test.)
If so, then your best plan is to study for and take that test first, and then take the GMAT after that. The preparation for the first test will help you to build a good foundation; the GMAT will require an even more sophisticated level of language skills.
If you are not required to take the TOEFL (or equivalent), then you'll be looking at a longer-than-usual period of time to study for the GMAT.
I would start with something like MGMAT's Foundations of Verbal Strategy Guide. Once you have mastered that material, you can move on to the main Strategy Guides for SC, CR, and RC (or something equivalent from another company) as well as the Official Guide materials. (Alternatively, you can also look into taking a class or working with a tutor.)
Can I ask why your goal is a 750? No school requires a score that high, and no school will reject you for a 700+ score (though they could reject you for other reasons! :). It's quite a challenge for anyone to score at that level (by definition, only 2% of all testers score at that level or higher).
Here are some free resources to help get you started:
https://www.manhattangmat.com/blog/inde ... lly-tests/http://www.manhattangmat.com/blog/index ... an-part-1/http://www.manhattangmat.com/blog/index ... -the-gmat/If you eventually take an MGMAT CAT, you can use the below to analyze your results:
http://www.manhattangmat.com/blog/index ... ice-tests/Then you can come back here and tell us the results of your analysis and what you think you should do based on that analysis. We'll tell you whether we agree and advise you further. (Note: do share an analysis with us,
not just the raw data. Part of getting better is developing your ability to analyze your results - figure out what they mean and what you think you should do about them!)