It is neither too easy nor too tough to get a 51 on the GMAT Quant section. To develop any skill you need hard work, dedication, time and adaptive learning. Hard work and dedication can be brought by with motivation. It is adaptive learning that can guarantee you a 51. Now, you cannot get a 51 on a bad day, but we can convert all our normal days to 51-scoring days. This is why a 51 score indicates excellence. The following will help you to guarantee a 51:
1) Learning from each mistake : 33% of the time should be spent for practicing and the rest for reviewing the mistakes
2) Carrying more than one technique: You can't rely only on basic algebra skills to get the right answer. There are various other techniques such as Plugging-in Numbers, Back-solving and Ball-parking, which will help you tackle tricky situations that can make or break a 51 score.
3) Double Checking: If you give an extra 10 seconds to a question to double check your answer, the extra time will be worth it. There are many techniques to double check. For example, whenever you get an answer, double check it. I 'd say that 10 % of the times, you will see a mistake.
4) As Sir Alex Ferguson says, "The hardest thing is doing anything the first time." So once you get a 51 in any test, getting the second 51 won't be that tough.
If you follow all the above, then only a bad day will stop you from scoring a 51. Over time, 51 will become the new normal.