It really varies. I like Tenderisers response regarding offering your first free book and then luring in more readers that way. It's hard to get new readers as a new author, but there are always readers who would be open to new authors. I always check if there's a new writer in the fantasy genre. And like many others, I also look for free stuff on amazon. It might be enough to get me into your series. Nobody's going to have an exact calculation and the biggest pain in the butt is having a marketing strategy. Also, you have an option of setting your book for a certain price on there and I believe amazon takes a small percentage per book sale so there really isn't an easy estimate on sales.
Hi, People use freebies as a promotion strategy with varying degrees of success. It used to be over on kindleboards that they raved about it as the way to make money, but the algorhythms have changed and I think those days have gone. I don't do it personally, but then I don't do much of anything promotion wise. My understanding is that if you're going to use a freebie as an incentive the best way to do it is to do it for the first book in a series - when you've published the second book and not before. You want people to read the first book then look for the second, not wait for six months and forget about it. Go to the writers cafe at kindleboards and you'll find a lot more threads on this stuff. Cheers, Greg.
When it comes to book sales, I would say the priorities are 1) Knowing how Amazon works, 2) Having an appealing cover, 3) Having a good blurb.
At the beginning of the month I published a book on Amazon under my pen name. So far I've made the grand total of £4.50. I also put it on Smashwords and only sold one copy. My experience so far is that Amazon earned me more the first few days of release, but now has dropped off to nothing. I will be trying out the Kindle Unlimited option soon and see how that compares.