I think getting to the top ranked books on Amazon is rather complicated. Often I have to find a random, then click my way to find the top amazon ranked books. Then I came across this website, http://ebooktop100.blogspot.in/ They have laid out rankings for easy access. though I am not sure how exactly they get the ranks. They seem to doing their own inhouse ranking algorithm. Anyway worth taking a look.
They even have a list of kindle authors have sold a crap load of books. Informative. I wonder what I can glean from that. Yeah, write something someone would like to read. Stop use writing as mental masturbation. Yeah… You go look on to find their bestseller authors lists. You tell what I need to learn from it.