It's often used to describe something that's well-maintained or that looks new and modern.
Here are some examples:
* "That's a spiffy new car you got there!"
* "She always looks so spiffy in her outfits."
* "I'm going to get my shoes shined, I want them to look spiffy for the event."
"Spiffy" carries a positive connotation and is often used in a playful or lighthearted way.