More specifically, an e-book. I know some markets tend to have season changes which make a certain time of year more beneficial for sales, but I was wondering if anyone had noticed anything similar with books? I know there is always a big increase in sales around Christmas, but are there any other periods where writers might see an increase in sales? Also, knowing that Christmas is the biggest selling period, when would be the best time to release a new book to try to take advantage of the upswing?
eBooks only really "exploded" in sales over the last couple of years, so there likely isn't enough data yet to be able to accurately say what periods of the year would be best for eBooks. eBooks may not follow the same trends as normal books, after all. I'm not sure if people are as likely to buy an eBook as a gift for a friend as they are to actually buy a physical book, for example, which would mean Christmas periods may not be as good a time for eBooks as printed books. Then again, eBook sales may correlate with sales of eBook readers, thus the period just after Christmas could be a big time for eBooks.
Logic would also suggest that those times of year when people go on holiday would be the best time, since they would be stocking up on books to read while away. This will differ from country to country, obviously, but a tentative guess would suggest that's a good time to focus on.
Also worth mentioning: I recall reading that a printed book must shift in stores within 6 weeks. Unsold books will be returned to the factory within 4 months. This would suggest that getting a printed book into the stores for the Christmas period should happen around November/early December sometime, but I'm sure someone else around here involved in the industry will have better knowledge of this.
Of course, the best advice is that your book should be released when it's ready. Don't rush it. Finish it, be happy with it, publish it.