Audiences are good at recognising genre tropes. The only times you truly shock your audience will be in the moments your story subverts the expectations they have formed about the story’s genre. Use this fact to your advantage. Pick a story trope, hint at it a little, only to completely subvert it—you can repeat this trick endlessly. Lead your reader down a road they think they know. As they recognise the ostensible ending in the distance and walk towards it, they don’t see the unexpected hidden trap you’ve laid at their feet.