A feel of the setting. As soon as a reader opens the first page, they need to be immersed in your world, no matter how significant the setting is to the story. If you’re bouncing between ideas, pick a setting with strong imagery and sensory details. It helps to take the primary emotion of the scene (e.g. if a character is being chased, the primary emotion would be fear) and use it to color the scenery (wind/rain/thunder, darkness) and sensations (flashes of color, conversations blurring together, heart pounding, panting). These will tie your theme together and draw your reader in, as well as inspiring empathy for the POV character.
Information about the main character. Don’t see this and jump to infodumping, though – no one cares about your character’s MBTI at chapter one. But they do want something to let them know who they’re dealing with. Take a predominant trait and let us see it and feel it throughout that first chapter, so we feel like we’ve learned something. It’s like when you meet someone at a party! If they share too much, you’re uncomfortable; if they share too little, they’re just “that person whose name I forgot.” But, if they’re that guy with the big hat, or that girl who kept shouting “You communist!”, then it’s a lot easier to remember their name is Sam.
Something obscured from the reader’s view. Your first chapter risks functioning as a short story, or “that interesting book I started but forgot about,” if there isn’t incentive to keep reading. You need to answer a lot of questions, of course, but you have to leave a few unanswered. Take the mystery of your plot (and if you don’t have one, that’s another ask entirely) and drop us right into it – even if it’s something small.
A taste of what the story will be. The first chapter should be interesting, exciting, yes – but it should represent what the story is, so think about the whole story for a minute. What’s the genre? Who are the key characters? What’s the arc and the plot that we need to look for? It’s like a first date – you want to look good, of course, but if you misrepresent yourself, the relationship won’t last. Let the readers hear your author’s voice, loud and clear, and let them know what to expect from here out.
Stakes, stakes, and more stakes. Mystery is one thing. Not knowing what might get you is one very good thing. But knowing for certain that something is out there – something bad is going to happen and it’s only a matter of time – will turn pages for you. Even if we don’t know exactly who the character is or what they’re facing, let us feel that nervousness of, “What if she does this? “What if he doesn’t get there in time?” “What if he never breaks up with that girl?” Otherwise, you’re advertising a merry-go-round, and that’s never as popular as a rollercoaster. I know that from Rollercoaster Tycoon too. Seriously, merry-go-rounds make garbage money.