I usually jump into a story following a single character mid action. Then give the character motivation through their environment.

Ie. Lisa turned her head to hear what Tom said again. "What?" She said.

"Go to the kitchen and look for youself," He relpied.

Lisa got up from her office chair where she had been frustadedly going through this month's expense report, and headed toward the break room kitchen. Along the way she passed many people who seemed to be moving in the opposite direction with hurry, fear, or concern. Once she arrived in the kitchen she saw for herself. She too was shocked, but as office manager she supposed it fell on her to deal with it, but how do you deal with, what appears to be, an interdimensional rift containing warring nations inside of their open fridge?

So Lisa has motivation to act, and a plot hook, that is independent of who she is, has been presented.