I've used a technique called the Amazon Bestseller Campaign, and it works really well. Here are some tips:
1) Write a book of real value for a specific market.
2) Know who that market is.
3) Figure out where they are online, and lots of ways to reach them.
4) Create a lot of bonuses to give out if people buy your book. Set up a web site where the bonuses can be downloaded for free.
5) Get the word out that, if people buy the book on Amazon in a limited time, they get lots of stuff for free!