1. Give your character something to lose. Any decision they make will cost something, whether it's their reputation, a friendship, a vision of how they saw themselves, etc.
2. Ask yourself, what could go wrong for him or her? When things are going along smoothly, how can you create a twist in the journey? Can you give her a time crunch?
3. Have conflict attacking the protagonist from several directions. I had my protagonist's bad decision affecting her relationship with all the important people in her life but for different reasons. Each character has different motivations and it's the conflict of those that can lead to tension.