My daughter has an interesting habit. As I read her a complex story, I'll read her the first sentence of some paragraph... for example, "The war news was terrible," and she'll instantly ask, "Why?"
Sometimes I find it charming. Sometimes it derails me and I don't find it so charming. But tonight I realized that she is acting out what we all experience as we read a good first sentence. The first sentence of a book - even the first sentence of a paragraph - should make us curious.
When I had my minor epiphany tonight at storytime, I explained to my daughter that she was experiencing something very true about stories. She had caught (and verbalized) the precise sensation the writer was looking for, and that she would learn the answer to her "why" question as I continued reading, if she could just be patient. My son seemed rather crestfallen to think that he didn't do the same thing she did - but I said maybe he just didn't do it aloud, that he might be doing it in his head as we went along. His eyes went wide. "I am!" he said.
Look for that "why" as you write. It's not necessary with every paragraph, but it should pop up regularly. Check the first sentence of your book, of each chapter, of each scene. "Why" is your hook. If a stranger can read your opening sentence without a single hint of curiosity, you may have revisions in your future.
It's something to think about.