Imagine the worst possible day of your fictional character’s life. Start when he wakes up in the morning–what’s the worst possible circumstance he could find himself in the moment he opens his eyes? Go from there. If you ever stumble and aren’t sure what could happen next, just start listing possibilities. You can go back later and pick and choose the most effective.
Difficulty: restrict yourself to ordinary, everyday events. Sometimes writers think something extraordinary has to happen to their characters to push them over the edge, when often it’s the most mundane difficulties that add up: a sick spouse, a power outage at a critical juncture, a fridge full of spoiled food before a party, a patch of unnoticed poison ivy in the garden, etc.