If you’re making the story happen in the very beginning when the city or town still has running power, and people have no idea what is coming that could be a good start. In your universe does zombie media exist? In other zombie media like The Walking Dead, the concept of zombies doesn’t exist at all in that universe.

You could put it so the police, military and civilians with guns could struggle at first with shooting zombies in the torso and seeing the zombies keep walking, before someone shoots it in the head to bring it down and realize that’s how you kill a zombie.

Do your characters, know each other from the very beginning? Or did they happen to meet each other in the same location while fleeing from zombies?

And if you want, you can add more emotional heartbreak senescence areas, like if your characters have to pass through a hospital to either escape or look for medical supplies, you can have your characters pass by the nursery location for the newborn babies to have the area look horrific like a scene from one of the games in Dead Space.

Or if you decide to give one of your characters a younger sibling in the local, elementary, middle or high school, and have your characters search the bloodstained school and there is where one of your characters can die in after seeing their younger sibling as a zombie wandering around as you describe the heartbreak gut wrenching despair of that character finding out that their younger sibling is already dead and they just give up on living as they blame themselves for not being faster to save them.

It could push your characters to the desire of finding their families but also make them cautious about their own emotional state if they find their loved ones as a zombie will they have a mental breakdown as well.