A great first line can really get your story moving. Stephen King has said that stories are found things, meant to be unearthed like fossils.
Here's some random opening lines off the top of my head. Feel free to use them. Maybe it'll get you digging on that story fossil.
"I awoke to a gun in my face and knew it was going to be a bad day."
"As I peered down the hole, it stared back at me with bloodshot eyes."
"This is how it happened."
"She saw the hooded man coming up the walkway and immediately locked the front door."
"He gazed upon his army, ten thousand strong, and prepared for what might be his last battle."
"Getting your ass kicked tends to put life's minor problems in perspective."
"As the van rolled past, she noticed the passenger. He wore a rubber Halloween mask."
"He'd seen his share of nasty homicides, but never anything like this."
"The new neighbor, yeah. That's the guy on the wanted poster I saw."
"As they rode up to the fortress, the dead lay strewn upon the ground."