There's not a whole lot I can say about first chapters (especially after what the others have said), but if you chose to go without a prologue, then there's a few points I want to make.
Give the reader a question. It can be anything, but something relevant to the overarching story. Things like "who's this? What's special about this girl? Why does a lightbulb appear above this guy's head when he gets an idea?" Despite never actually reading it, I like to use Harry Potter as an example. The biggest question was "what's so special about this kid?" I mean, being a potential wizard is pretty amazing, but that's not what the question was. It was "what let him survive the big bad as a baby?" The author takes almost the entire series to answer those questions.
Yours doesn't have to take so long to answer them, but the questions and answers should be relevant to the entire story.
Whether you start at the beginning or in-media-rez or not doesn't matter a whole lot, and is your decision though. Some prefer taking their time to get to speed, others want to jump right in. But there's a cheat to that: prologues.
The point of a prologue is to do a few things. First, provide the question in the place of the first chapter. Second, set the tone. Third, give information to the reader that the first chapter isn't able to, but is extremely important.
The first point is self evident.
The second is basically a promise. That promise is how the story is supposed to feel. Oftentimes the first chapter has a very different feel from the rest of the story because it's used to set things up. Maybe it even takes several chapters to establish the tone. But readers often don't have the patience for that, so they decide that the first chapter is how the entire series is going to feel. The prologue exists to tell those people "hey, this is how the story is going to be like, but we won't be there for a little while, so buckle up!"
I've read plenty of stories that spent 10+ chapters doing one thing before going on to how the actual story ends up being, and a prologue would've make me realize how the story was actually going to be like much faster. I wouldn't doubt that many readers saw the tags, started reading, then quit before those 10 chapters were up disappointed that the tags lied to them.
The third point is a bit more difficult, but basically you can use the prologue in ways that you normally couldn't write elsewhere, especially so early on. Things like the differing perspectives, or events far apart from the first chapter in time and/or space. It's very easy to tease things in the prologue that can't be dealt with in the main story for a long time. Either an event far in the future of the story, or far in the past that the MC won't discover for a while. It can be whatever you want, and readers explicitly understand that the prologue and first chapter won't flow fluidly between each other.
Anyways, that's how I feel about it. Prologues are amazing tools and extremely important, but not essential.