Spelling and grammar is a huge issue! Typos here and there are fine BUT try and polish your work off and avoid easy mistakes like not capitalising 'i.' Websites like ProWritingAid and Grammarly offer free editing which should nip most glaring errors.

Open with a cliche (yes, those pesky alarm clocks are still making it into books). You don't have to start at the beginning of the morning.

Dumping too much information in the first chapter. You don't have to tell us their whole backstory. Sprinkle that information throughout the book.

If you're struggling with your sentence structure, read it out loud. If you can't read it out loud, there's always headphones and Google Translate.

Overusing a certain work. She did this. I do that. He went there. Use descriptions to break up the constant repetition as it'll avoid your character sounding like a robot.