I admit, I never considered the following advice as a suspense secret, but I do now. And even better, it applies to EVERY genre even more than basic "suspense" techniques do, for the crime author's tip is based on character building.
I really encourage you to read the entire article, "How to write fiction: Mark Billingham on Creating Suspense," but here's a bit to wet your appetite:
"I am often asked at events and creative writing workshops how you go about creating suspense. There was a period when, in answer to this question, I would talk about the tricks of the trade: the cliffhanger, the twist and the "reveal". Such things are still important, but I have come to realise that the answer actually lies in something far more basic, something that should be central to the writing of any piece of : the creation of character.
"The techniques mentioned above are, of course, all vital pieces of the mystery writer's armory and, as such, are components of the genre that readers of crime novels have come to expect."
But . . .
". . . above all, give your readers characters they genuinely care about, that have the power to move them, and you will have suspense from page one."