Just recently, a writing friend, who, despite being an excellent writer, is having problems with her story's jerky feeling, asked me: "What do you mean by flow (big wail here!!!)?? I know how to recognize it in other people's writing, but I'm not sure what the specifics are. Is it a technique you can learn, or more a feely, intuitive thing?"
My answer is, It's hard work -- darn hard work! It's a technique, but I don't know of any tricks to get there sooner -- I'll just give you my journey. It's polishing and re-polishing, checking every scene and chapter to be sure they connect to each other. That's flow, and no-one can teach you. You have to go over your book time and again until it does become feely and intuitive.
A non-driver never learns to shift gears without thought, do they? No-one can teach you how to drive without thinking, in that second-nature way, to where you've been a hundred times. Story flow is the same. You have to know the bends and corners - the turning points of your book, and connect them to the theme, the romance, the depth of the relationship, until it's second nature, and you do it without thought, knowing instinctively where it isn't flowing and working on it.
In a recent a workshop, Fiona Brand said "to crystallize your story -- put it in one sentence. And connect your whole book to that one sentence." I agree completely, but while working on story flow, I try to go one step further and say, add your turning points -- but never more than two. Find your two biggest growth moments for the hero and heroine. If you connect these two together and make them completely central to the theme, plot and especially the developing romance, the book will flow.
In my latest book, the theme was that both hero and heroine wear masks: one physically, one emotionally, and both had to learn to leave them behind and accept themselves exactly as they are. The sexuality, the danger, the spying, was all secondary to this one intrinsic truth. I knew what I wanted to say. The two turning points were her telling him about her having been raped by a deranged fan three years before, and his telling her that she was running from the past - not just from the rape, but her childhood abuse by the people in their hometown. In essence, in becoming famous and re-inventing herself as "the Iceberg", she now wore a mask, just as he did. But hers was emotional, where his was physical, used for the safety of the mission they've been sent on together. At the end of the mission, he took his physical mask off, willing to face the world as he was, imperfect; she had to let her emotional mask go, let go of Verity West the Iceberg, and learn to be herself, Mary-Anne, again.
The theme and plot and relationship, the romance and sexuality, the danger and action, even their interaction with others, all had to hinge on this. It had to be everywhere, leading up slowly, building to these two pivotal moments. I kept them in the front of my mind throughout the book, and so, even though this book was the hardest I've ever written, the book flowed, because my theme and turning points were always there in front of me. And when I knew something was missing (besides the 10,000 words it came in short!), I thought again of these turning points, Fiona's words, and I knew what was missing. And the new scene flowed into the rest of the book.
So if you're having trouble making your story flow, find your one theme. Put it in that one sentence, as Fiona says. Find your turning points, your two critical points that make your book unique. Write them down, and keep it in front of you as you write every sentence, every scene, every chapter. When the book's that simple, in that one perspective, all else will flow. It's hard work to start with, but it's well worth it. It's second nature to me now.