As a short rule of the thumb I suggest but if you have three questions you have enough to begin with. So once you have 3 questions stop previewing or post viewing and start activating.
If you don't have any questions during the preview. That's okay, consider shortening the preview of that particular book, PhotoRead it and do a post view were you pull trigger words and build your curiosity, asking questions. Once again once you have three questions you have enough to begin activating.
Just pull trigger words during preview. That is, if you are previewing for more than 90 seconds. You will find it much easier form questions during a post view.
AlexK
