If someone says your writing needs to be more "mature", then the solution to that is to include an endless deluge of rape, major character death, self-harm, brainwashing, and other similar subjects. I don't know what the word "edgy" means, but the more times that people in the comments use it to describe your story, the better it is.
If you want to write about something you don't know much about, just take a quick glance at the wikipedia page for it. Don't learn too much about it - nobody likes a know-it-all.
Make as many pop-culture references as you possibly can, ESPECIALLY to current fads like the newest dance craze or some funny picture that's been making the rounds this month. It doesn't matter if your story is set in the past where these things don't exist.
If you make a typo, don't bother correcting it - consistently make that same typo throighout the entire book. People will just assume it's a dialect or something.
If you need to make a cool, badass character, replace some of the letters in their name with numbers. l1k3 th1s.
If you aren't sure how to spell a word, just write every spelling you think it could possibly be, one after the other. It won't come off as nonsensicle nonsensakul nonsentiocle nonsensecal.