Ever read a book and go ... Ugh! I'm so bored where is the suspense? I had this happen a few days ago. I won't name the book because people might like it or love it and I'm not here to sway opinions. I am however trying to tell you as a writer you need to have a smooth flow of things. You can start a book many ways, Action first, leading to a calmer get to know the characters, and climb back into some suspenseful event and build from there. That's fine. You can also start out with a calm relaxed scene opener followed by a WTF shocker and build from there. There is a lot of ways to do this, but just keep in mind how long the calm and relax setting goes, when you build to the shock. And even the action to calm there must be a point of process and evaluation on the reader. They must be able to say I hate this person love this one, and so forth before moving into the next phase because, if the story moves too fast the reader can't tell if they like the characters and none of them will be memorable.
I want to stay up reading not be put to sleep ;)