OUR SUSPENSE TOOLKIT
Use an abandoned setting or lull the reader with a cosy setting, for example

The pond glittered. Daylight filtered. Bees bused. Dragonflies flittered.
Personify the setting to make it sound dangerous.

For example, Thunder growled overhead. The branches reached towards her. 
Scary place names-

For example, It was known as Deadman's Forest.
Use the weather and/or time of day to create atmosphere 
For example, Dark clouds loomed. An owl hooted. 
Make your character hear, see, touch, smell or sense something ominous 
For example, A door banged.
Surprise the reader with the unexpected-

For example, It was just the cat. Phew!
Drop in warnings-

For example, The crows cawed their warnings as she sauntered amongst the trees. 
Use deadly ideas-

For example, The rain danced a thousand deaths on the pavement.
Suggest something is about to happen

For example, She shivered but not from the cold
Reveal the character’s thoughts,

For example, She wondered if she would ever escape the darkness. Her imagination was playing tricks on her.
Slow the action by using sentences of three and drop in clauses. For example,  
Nearer and nearer it came until the cat paused inches away from Jo's hiding place and sniffed. Jo paused.
  Hide the threat -For example, All she could hear was silence that filled the house with sleep.
Use empty words such as silhouette, moved, empty, nothing, shadow, something. 
Ask a question -What was that?

CAN YOU ADD YOUR OWN 'KEEP IT' SENTENCES.