Any tried PR first? I think I have. The first day of the 5-day plan is just prepare/PR. You don't preview the book until the second day.
Cues? I struggle with this one still. You're looking for your body's own intuitive signals. In the past, when you've had intuitive flashes, how did they come? Encourage your inner mind to give you similar signals (feelings, images, sounds...) to indicate the useful information.
Overdipping? A constant struggle for me because I LOVE reading. As soon as the information no longer seems directly relevant to your purpose, stop. For instance, you're getting three more paragraphs that substantiate the useful nugget you already read.
Mindmapping? Go for the concepts that are key to your purpose. You can mindmap too much, just like you can dip too much. Don't worry about mapping every chapter. Map the stuff that seems useful to you as you dip. If you want more info, look for: The Mind Map Book by Tony Buzan, Mindmapping by Joyce Wycoff, or the tape on mindmapping by Michael Gelb. All are excellent resources.
I would argue that you aren't just going for main ideas with PR. You can get that from reading the jacket of the book and looking at the table of contents. Hopefully, with PR, you are quickly getting the information that is relevant to your needs.