I don't think you have to have well into the 90%s, but I don't know for sure, I'd say it's probably necessary to get into the 800s to be seriously considered by most top 10 schools though. I retook the test after getting a 780 last year (ok, it wasn't so bad, but I felt like it was at the time) and was able to improve my score by 200 points after just spending a good bit of time studying during the summer.
Basically my study method revolved around working multiple choice questions like those listed here
to improve my speed. Also, I would write down the equations (finding them in my textbooks from university) which were necessary to solve these questions on flash cards and work on memorizing them. Usually, I would use the ETS practice tests to gauge my progress and/or to motivate me to study harder when I did really poorly on them.