Okay I’ve never published anything so take my words with a grain of salt. A few good things to do is make your description capturing, maybe include a quote from the book or a song lyric that describes it. Add a cast at the beginning because that also excites readers especially if they know an actor or something. When it comes to actual writing maybe map out your story with its rising and falling action and all those components, and try and make your story unique in some way. In my opinion long chapters are best but a short first chapter can also be nice for new readers. Idk I hope this helped!