GRE score is very important in the admission process, but fortunately and unfortunately it is not everything. Just because you have a low GRE score, it does not mean that you cannot get admission in a good program. Similarly just because you scored high on the GRE, it does not mean that you are guaranteed a spot in a good university.
This difference exists because US universities look at an applicant's profile in a holistic manner i.e. everything from the strength of your purpose and maturity (evident from the SOP), to the strength of your academic scores to the Letters of Recommendation received will be considered along with your GRE scores while making a decision.
So, if for some reason you have score low in the GRE, there is no need to lose hope, by making the other parts of your application very strong, you will give yourself a much better chance to getting an admit from a high ranked university.

Methods to Improve your chances of an Admit from a High Ranked University:

• SOP: The statement of purpose which you write is of paramount importance if your GRE scores are low. The SOP is your opportunity to show the admission committee that you are a professional and serious student who has clear goal in life. Additionally since you will never talk to the committee (in most cases no interview will be required), the SOP will act as your opportunity to talk with the people in the committee. If you write an excellent SOP which impresses the professors reading it, chances of you getting an admission will be increased drastically.
• Prior Research: If you are applying for the sciences, use every opportunity you get to do research on your topic of interest during your undergraduate. If you can publish in a respectable journal, even with a low score chances of you getting admitted are very high.
• Work Experience: If you are applying for other streams where publishing your work is not possible, get as much work experience as humanely possible. Do internships in a respectable company during your semester holidays and work part time if possible.
• Undergraduate Academics: At the minimum maintain a GPA higher than 3.2, while a minimum of only 3 is required, a high GPA will never hurt you!
• Letter Of Recommendation: Along with your GRE scores, SOP, and academics, the strength of your LOR's matter a lot. More important are the people who are writing the letters. So during your college years be on the best behavior with your professors, even a single bad LOR can lower your chances of admission drastically.
• Final year Project: Do it in an excellent government institution if possible. This is good in two ways; firstly the chances of you doing novel research and getting a publication will be very high. Secondly a letter of recommendation from a government professor carries much more weight (for example an LOR from an IIT professor will be given more importance to than a normal LOR from a professor in a normal university).
• Extracurricular Activities: While academic endeavors take precedence when making a decision, if you can both maintain high academic scores, and at the same time participate in a number of extracurricular activities you will be viewed far more favorably than other applicants (Note it will be considered favorably only if you have competed in the state or national level, have medals and certificates to prove it!).