Getting into the top universities is not as simple as doing well on the GRE. There are many aspects of the application process that need to meet the minimum requirement for each college. Not only that, the requirements vary depending on which stream you are applying for even if it is the same university.
One such requirement is your essay or your Statement of Purpose. The best bet for you would be to attend GRE coaching classes, to develop not only your quant and verbal skills but also acquire sufficient information about the application process.
However, if you want to know what a good or rather a competitive score is, it varies for each college and the stream that you are applying for.
On average a 315-320 on the GRE should get you through into most of the good schools.