No matter what type of book you write, ask yourself what will be the readers first impression?
If writing a series of short stories-put your strongest story first, especially one that that has a good opening.
The same applies for any type of book. If you write a teaser or overview, really think about why anyone should want to read your book. People desire to have something at an emotional level and justify buying at a logical level. Therefore how does your book ‘speak’ on an emotional level?
Then once you feel you have satisfied this part, look at the next part. Does your book meet someones expectations on a logical level?
For example, can the purchase be justified? Here price, value for money etc come into effect so you need to have all these boxes ticked too.
Your book should be professional from start to finish. It should be professionally edited, properly formatted, with a good story line, with good structural flow, but the first few pages really are critical to forming a positive opinion of how they will perceive the rest of the book.
Remember, if you are publishing on Amazon, a reader will be able to view a sample of your book and download it to their reading device, hence the importance of ensuring they get to sample the best of your work. You want to entice them so they will want to read more and ultimately buy the book.
Same goes for books submitted to Smashwords, the largest ebook distributor in the world (which distributes to Apple, Waterstones etc). Except here, you as the author get to decide how much of the book can be sampled before purchasing- 10%, 20% etc. Again work out how many pages of your book this equates to so you know what is included in the sample.