Some writers can hardly write at all, but they can plot like nobody's business. I recently finished rereading Ken Follett's The Pillars of the Earth, which I'd assigned to one of my creative-writing students as an example of blockbuster historical fiction, and which I decided I should actually reread, too, if I intended to comment intelligently on it. Reading it was very enjoyable in an undemanding kind of way, like reading a 1000-page magazine, and most instructive in the craft of how to write your average million-plus seller. Follett, who has in fact sold about 100 million books since he got started in 1978 with The Eye of the Needle (later made into a pretty good movie starring Donald Sutherland), understands the rules of bestseller-writing better than most. Basically, they can be refined into a 10-point program: 1) Don't attempt to write with style. Plain, unvarnished wooden prose is what your reader expects, nothing fancy. 2) Never introduce any humor that isn't obvious, leaden, and faintly slapstick. Irony is a no-no; the reader will think you're being too clever by half. 3) End every chapter with a short, pungent, one-sentence paragraph: "The man was dead." 4) Start every other chapter with a similar one-sentence paragraph: "By Christmas they were starving." 5) Economize on character development. All characters are basically the same, with differences in gender, height, and occupation. N.B.: The evil ones have to be shown being evil over and over again, preferably to the good ones. 6) So the reader thinks he's learning something, not just being entertained, overwhelm him with the minutiae of background detail, e.g., "The top quoynes of a cathedral are composed of octagonal stones three feet wide by two long, laid side by side in a process known as 'quoyning.'" Or some such. 7) Throw in an absurd sex scene every twenty pages, even if–as in Pillars of the Earth–it involves people who are starving, haven't slept for days, and have nowhere to live. Never mind; they climax magnificently. 8) Undergird your narrative with cliches, so readers will know where they are. People must know places "like the backs of their 
hands," and move "as quietly as cats." 9) If by chance you do come up with a halfway original metaphor, be sure to repeat it several times, e.g. "He raked the room with his eyes"; "she raked the landscape with her eyes"; "Their eyes raked each other." Finally, 10): Ensure the last chapter echoes the first, so we can all be satisfied that we've come full circle, and that no loose ends remain. In Follett's book, both the first chapter and the last feature a hanging, and both start with the one-sentence paragraph "The small boys came early to the hanging." 

I would be as incapable of writing like this as Follett would be of writing as I do. Mind you, he's sold 100 million books, and I've managed maybe 20,000. So the moral is...?