Most of my Ah-Ha moments in writing came when reading either the Greats or the Trash. Now capital T Trash is not confined to genre, as some snobs might dictate, but can be found in everything from horror to the shelves so generically labelled "Literature" at your local big box store. But there was an epiphany that started to form in reading Hemingway and Le Carre and "`Salem's Lot," as much as it started to form reading bad gorefests and pretentious purple prose that sought more to obfuscate than to illuminate. You should read mostly good books, of course, but reading bad books can show how NOT to do it.
And it, in this case, is tension. The epiphany, which, to be honest, was less of a lightning strike than an electrical hum growing louder over time, was that tension was an art unto itself. It required a few major pieces, but the biggest seemed to be patience. To truly build tension, whether it's in an Elmore Leonard crime caper or a Geoffrey Euginedes story of family, required patience on the part of the writer. You had to be willing to dole out your brilliant story in small pieces that might, on the surface, seem inconsequential. But as they began to stack up, the reader got hooked. They had to know just what puzzle these little pieces they're being given came together to complete.
Sure, there are other components. A healthy dose of paranoia, for one. Mood and atmosphere for another. And character, let's not forget that. But where most of the Trash got it wrong was with pure impatience. The authors of those bad books had ideas they wanted to get across and couldn't wait to put them on the page. Thus, when the tension was non-existent, it was primarily because I had all the pieces to the puzzle too early. I don't care how phenomenal the climactic fight is or how horrible the monster is when confronted if the tension doesn't pull me along to those scenes.
It's a bit like sex without foreplay. Sure, it'll scratch the itch, but it isn't memorable.