With Lacey (this doesn't work for the "stop and spin" kind of spooky horse but for a "stop and stare, then approach" spooky horse, like Lacey, I've had this work great), on the rare occasion that she starts getting all shifty eyed, I've had luck with asking her to stop before she actually spooks (when she's in the "head is going up higher and higher" stage) and watch whatever she's worried about. After about 30 seconds, I can usually feel her relax and she'll generally start approaching whatever it is on her own. I allow her to approach and I act confident. On the ground, I confidently march ahead like I know exactly what I'm doing and where we're going, and in the saddle I give her a pretty loose rein and have constant contact between her sides and my legs until we pass the scary object.
If she just spooks, I act like nothing happened. I just keep doing whatever I was doing like she didn't just leap into the air.
However, if she spooks out of nowhere and continues to act jumpy, I'll have her stop until she relaxes, then urge her forward in a confident manner.
It's all about being confident. The more confident you are, the less spooky your horse will be, and the more he or she will trust you for guidance in an actually scary situation. I'm a firm believer in "fake it 'til you make it". Just act like you believe you're the world's best leader and eventually your horse will believe that you are the worlds best leader, thereby confirming your sneaking suspicion that you are, in fact, the world's best leader!