The thing about writing I’ve found as an editor is that if you are struggling, it’s because you’ve lost your focus. Think about it like I’m your word doctor and you’re my patient. You come in with symptoms (struggling with writing). Without checking your temperature or anything, I’d diagnose you with lack of focus.
You either haven’t started because you don’t know how (i.e., you haven’t defined your topic enough) or you have written a lot and are stuck (i.e., you haven’t defined your topic enough).
Either way, you need to figure out what’s important. Kind of like life, actually.
So get a cup of coffee or tea, or a glass of wine or beer, and sit down with that screen. If you haven’t written anything, start with your outline. Pretend like you’re emailing your best friend or your mom to tell them about something new. Write out how you would do that. If you have written a lot and feel like you don’t know where to go next, go back to the beginning and systematically remove all excess words. Play a game with yourself to see how many words you can remove or phrases you can replace with single words.