In the first chapter, you'll need to introduce your main characters and the main conflict of the story. By the end of the first chapter your reader should be able to tell what type of book you are writing (i.e. romance, suspense). And you will need to start the book with a hook. Make your reader WANT to read the book to find out what is going to happen.
Avoid backstory. Many new writers want to dump a bunch of backstory in the first chapter. Backstory stops the forward momentum of your story. Instead, show the backstory in little pieces throughout the book. This keeps the reader wanting to know more.
For example, I'll use an example from my novel FOXFIRE.
My first chapter has two parts. The first is in the heroine's point of view. The second is in the hero's point of view. The characters meet in the first chapter (necessary in a romance). Here are the last few lines in the heroine's point of view:
Grace rolled over and punched the pillow. She hadn't been a prostitute. Well, not exactly.
Get your attention? Make you want to keep reading to find out what happened in her past? This is what creates a page-turner.
Okay, now jump to the second part of the chapter which is in the hero's point of view. These are the last few lines of the first chapter:
Tyler couldn't bring back his wife or their baby, and he'd live with that loss the rest of his life, but he had an opportunity to avenge their deaths. He might spend the rest of his life feeling guilty, but he'd bring Max Clayton down, even if it meant using Grace Wilkins to do it.
Okay, now I have your interest. How do I drop backstory?
Here is part of Chapter 9. Grace and her Dog Tiffany have gone to collect the mail. She finds an envelope with no return address. I've left off pieces of this portion for brevity:
Curiosity got the best of her and she pulled the strip to open the envelope. Peering inside she saw a silk ivory scarf.
"What in the world?" She pulled it out and a piece of paper fluttered to the ground. The scarf draped luxuriously across her arm. The silk shimmered in the morning sunlight. She ran her hand down the length, its simplistic beauty mesmerizing her. She loved the feel of silk.
Tiffany sniffed at the paper that had fallen at Grace's feet.
Grace stopped and picked it up. The words scorched her vision. Printed in block letters was a name that made the bile rise in her throat. Gracie Jo. Only one person had called her that--the man she'd been hiding from for three years--Max Clayton. She read the note again. Gracie Jo. I know you like silk. This is for you. A gift. Like old times. How did you like the roses? Weren't they pretty? Such a vivid shade of red. The color of fresh blood.
She wanted to run back to the house, lock herself inside, and cower under the bed. She had thought she'd be safe here, but nowhere was safe. Not even Foxfire. And that meant...tears stung her eyes...no one was safe. Not Brad, nor Harri, nor Tiffany. And God forbid, not even Tyler.
Grace actually tells Tyler the story of how she met Max, and what happened between them, in Chapter 9. This is done in dialogue. The stakes have raised and in order to find Max, they will have to be honest with each other. However, if I had dumped all this in the first chapter, there would be no surprises for the reader.
So, what are you waiting for? Take those characters you've developed and that story that's buzzing in your head and take the plunge. Write the first chapter. Once you've accomplished that hurdle, the rest will be much easier.