Varies from applicant to applicant. But the most common ones in my experience are
1. Lack of persistence
3. Reading comprehension
4. Attitude. (Start looking for the amazing things on GMAT, and it will start occurring to you differently).
5. Do not fall in love with the test (YES !). Stay committed to it. Good/bad days, discipline should not be hindered.
It will roughly take you 350 hours.
Pasting my other suggestions directly from another response I gave on Quora
In as much as I know, there are no shortcuts to GMAT or any other test for that matter. However, a lot depends on how much ahead of the game you are already.
If you are considering self-study, I will recommend doing the following:
1. For MATH: Get a 51 on Quant: And in order to do that, start exploring the 700 to 800 level series questions. Start with the basics (GMAT NOVA), and then move over to the official GMAT Guides (Get all the editions) and practice them end to end. Remember: The official guides will not be the only source of doing maths as they are not very representative of the toughest questions, but they will still form a strong background. Once you are comfortable with the official guides, start over with the tough questions across whatever sources you find on the internet.
2. Verbal: For reading comprehension, start reading different sources of blogs. That is what we have been recommending to our students as well at PythaGURUS Education. Even if you are not seeking external help, you should try doing these things yourself. There is a very interesting MAPPING technique and it enables you to read diverse topics (Biology, finance, social sciences, literature, with equal effectiveness). Remember: When you read a passage, you should focus more on the key inflection points as opposed to getting immersed in details. When you practice questions across various sources, remember to finish the first 4 questions of any passage within 7 to 8 minutes.
For sentence correction, always have an error log. As you will realize, they do not have unlimited error categories. Once you are done with the theory across the 9 topics of sentence correction, start practicing the questions. You should spend as much time in responding to these questions as you spend in solving these questions.
Remember: You need to get a stable 750 on the practice tests in order to score a final 700+ on the main test.
In our experiences, what the students tend to do as they prepare:
1. You tend to pick up areas you score high in and stay around your comfort zone.
2. You tend to ignore the sections that scare you as you know it will make you upset.
3. If you score lower in your best areas, it takes your life away and you tend to stay away from the books as you know that you need your time to “THINK OVER WHAT HAPPENED”…although I really do not know what is it that you think about. I also am aware that you do not know it.
4. Your performance in the underperforming areas tends to affect the performance in your ROCKING areas as well.
5. In one month, your time spent in your difficult areas is way less than that in the amazing areas.
How should your preparation look like? (If you are not in love with the test but are committed to delivering.)
What they should be doing?
1. You will create a study plan (You can create a monthly plan and have weekly checkpoints to assess your performances).
2. You will give an optimum number of hours for each of the sections.
3. You will spend roughly 20-25 hours every week in 5 areas of GMAT. Half of this time will be spent on solving the questions, and the remaining half will be spent doing something even more important, Analyzing your exercises (both correct and incorrect questions).
4. If you start achieving amazing accuracy rates in some of the areas, you will continue to sustain those, and continue your weekly practice sessions rather than switching gears. If you tend to ignore your strengths, they tend to ignore you before you know it.
5. You will have self-study sittings of 3-4 hours split across two different sections (RC, CR, SC, DS, PS).
Go for IT!