Initially, the results were pretty good as finally something was moving. I published my first book in early 2011 and did not sell a single copy in the following months. But the moment I began offering books for free, sales started. A problem then arose because later the KDP Select program no longer worked as well as it had at the beginning. At that time I was not using Twitter for additional promotion. An example: in January 2012, I was offering the book Only the Strongest Survive for free and roughly 500 readers downloaded it within four days (every 3 months, you can spend 5 days promoting your book). Only one day was left. I decided on a Sunday. To my surprise, approximately 13,700 readers downloaded it on that day. You can read about it in my BLOG. Why that happened, I do not know. Consequently, I sold 707 books in January, as you can read HERE. But the fact remains that a great deal depends on what else is on offer and the way the electronic system on Amazon happens to be working at that time.
When in April 2012 I offered the same book for free, only approximately 90 readers downloaded it. This meant that the method was no longer working as it had in the beginning and so I decided to leave the KDP Select program, especially because Amazon was getting on my nerves by constantly warning me that my books were for sale elsewhere (Smashwords, Barnes & Noble, Sony, etc.).
Later I found out that, in addition to the KDP promotions, you must include social networks, such as Twitter. Only then will the KDP program bring you good enough results.