On building emotionally fulfilling suspense.
Suspense is mostly about seeing something coming before the character is aware of it, and getting excited on behalf of the character.
There are innumerable ways to show the reader ominous happenings are on their way.
Effective Suspense (Good Writing):
The clouds about LuEllen swept apart in strange patterns, as if beaten by conflicting surges of wind. A roar that rumbled like thunder made the ground under her horse tremble. LuEllen’s chestnut mare threw her head up; her forefeet lifted off the ground.
LuEllen leaned into her mare’s neck, and made soothing chucks with her lips; she stroked the shining red neck. Her mare’s eyes were rolling, showing white, and the mare’s hooves rose and fell with anxious thumps into the grass.
A strange, other-worldly rumble, like the keening song of a whale, echoed through the clouds above the shadowed valley; LuEllen looked up, and saw the barest flash of pearly green wings, as big as mountains, cut through the obscuring mist.
LuEllen’s heart skipped a beat. Dragon.
Ineffective Suspense (Bad Writing):
LuEllen turned her chestnut horse into the darkened valley; the clouds were low over the trees, and rain threatened to fall. LuEllen thought she saw a flash of shadow traveling over the long grass. There is no sun to cast a shadow, she thought, and looked up.
A great big dragon, pearly green in color, soared through the heavy clouds, like a massive whale cutting through water.
Give your reader at least three large clues to the foreshadowed event; let them get tingly inside before the big reveal.