This is a question we get every year, as candidates walk away from their GMAT test date wide-eyed and shocked that their score came in 50 points under all their practice exams.
You will surely hear over and over, that the GMAT is only a portion of your application, albeit a fairly important one. We have seen firsthand that top schools are not always lenient on incoming scores because the average GMAT has a big impact on the schools' rankings and they can't afford to slip from the coveted top 10 or 20 slots they so desperately try to hold. Even lower tiered schools are beginning to see their GMAT scores climb, and every school likes to see their average score go up each year. Last year, Stanford's average topped 729!
If you take a close look at the numbers, it is likely that your score, although perhaps disappointing to you if it was below the posted average, may still be in the 80% range of top schools, so don't be discouraged. In order for them to offer a seat to people with scores in the lower part of that range, however, you will need to be bringing something "else" to the table that is unique. Ask yourself what you offer that is out of the ordinary and stands to potentially add some level of diversity to the class makeup?
This diversity could come in almost any form, not just the obvious racial, cultural or professional diversity. Have you ever done anything unusual that impresses your friends and family? Well, it might just impress an admissions committee as well. Overcome a monumental hardship in your life? Achieved something truly out of the ordinary? And don't think it must have something to do with your professional goals, either. An unusual hobby or pastime about which you can relate an interesting story, especially one which has shaped you as a person, can sometimes also capture the interest of the admissions committee.

Additionally, your post MBA vision and career goals will need to be clear and sensible, and your overall application must be tight and impressive. Consider the help of someone you know who has an MBA to look them over before submitting, or get help from a professional consultancy like Veritas. Lower scoring applicants must do all they can to go the "extra mile" on their applications in order to stand out in the crowd, but it can be done with the right elements to balance it out. Good luck!