Depends on what series!
The Lacuna series are sci-fi novels. I tend to put them out at a rate of about one every six months, but I'm hoping to increase that in 2013 to three or four a year. Each novel is about 65-80k in length, and their structure is usually quite rigid. That is:
Three acts, a prologue and an epilogue. There are four chapters per act (except for Demons which used a three chapter x four act structure, which on reflection I didn't like). Each chapter is approximately 6k words.
The prologue is action filled and is designed to hook in the reader immediately (Demon's prologue is literally titled In Medias Res). Act I ends with a "call to action", there's a big twist at the end of Act II, climatic finish in Act III. Epilogue sets up the next book.
I price each one, including the first one, at $4.99. Since there's swearing and violence in them, I also put out a PG-13 edition, where the swears go down one level and, very occasionally, scenes get tweaked.
The Rakshasa series is actually a serial, so it's basically the above on steroids. Each episode is almost exactly 10k words, with 5-7 chapters, a prologue and an epilogue. Each chapter is much smaller, usually only 1k-3k words. They're pushed out much faster, usually fortnightly, but with moving house this month Shadowfall had to be pushed back by two weeks.
I play a lot more fast-and-loose with the structure of Rakshasa. How many chapters they have, their length, etc is essentially "whatever I feel like". I tend to write scenes out of order, usually starting with the end and working backwards, although sometimes I write linearly too. Essentially it's my book, I do what I want!
For the Lacuna series I find about 25% of people who buy the first book buy the next book, but sales on Book 2 and Book 3 tend to be equal. For Rakshasa, though, the subsequent sell-throughs are only about 50% per part (for example: 100 for Rakshasa, 25 for Aurora, 13 for Tigerheart, 7 for Shadowfall, etc). Could be just a wobble in the statistical average but this is really the first month I've had enough sales to be able to genuinely find a trend, so... yeah.
The Lacuna series has many spin-off short stories, but they don't sell much at all really. They do, however, have their own set of free days, which helps bring in new readers. So in that regard they're pretty useful. Faith is also perma-free, which helps, slowly working away in the background and generally passively bringing in new readers every month.
So yeah. That's my two series. Hope it was helpful!
I put out a prequel in October which is about 46k, but the other three books are between 87,000-92,000 words. I price between $2.99-$4.29.
