As you've discovered, letting people know your ebook exists, among over 4 million others, is the hard part.
Search these forums for the many many threads on promotion and advertising. No one method works for all, which is why there's no single answer. Read the threads and try various things. This of course assumes you've already made your book as good as it can be (cover, blurb, editing & formatting) and that it's in a popular genre. Good luck!
There are about 8000 new books published on Amazon every day. And it's July, this is down time for publishing. By October there will be more. Despite the overwhelming odds that nobody could possibly ever find my books, each month people do.
There is no silver bullet for selling your books. My best advice is to get the best possible product out there and then get back to the drawing board and write another. And another. It helps if you write in the same genre. I don't mean a series, the problem with series is everyone has to start at number 1 and it's likely that was not the best book. But just write more stories.
You can be distracted by constructing web sites and blogs and doing blog tours and tweeting and trying to get your reviews up and getting mail lists and then content for them but really, just write another book. I don't make lots from individual titles but collectively my work brings in a cheque each month I feel proud of. I always know I can do better and I put my energies into the next book. I sometimes go back and edit old work too because I find things I can improve. I welcome criticism from others.
There is a whole industry out there trying to take your money as an independent author. Don't get sucked into it.