If I were to sum up suspense writing, it would be: quiet, quiet, quiet, LOUD!
They often feature brave, curious, even troublesome characters setting foot in narrow, dark, quiet places, with a scary beast lurking in the background.
You’ll notice the beasts don’t appear until late in the story. Even then, they emerge gradually: a claw, an eye, a fang…
Up until then, they are just shapes or shadows. We know what will happen… our character doesn’t!
I have left the endings as cliffhangers. You can, too. Or, maybe you could change it to suit you!
A few useful Suspense tips:
Use repetition to build excitement or drama: the more, the more; closer and closer.
Use short sentences for dramatic or exciting parts: She ran. They had gone.
Use empty words: something, a shadow, a shape, a figure.
Use onomatopoeia words to build suspense: crack, click, rattle, snarl, hiss…