When you're reading, imagine yourself writing it. Try to understand what the writer was thinking when they wrote it. Focus on the things you like. Think about why you like them and how to produce the same effect in your own writing.
When you're writing, imagine yourself reading it. Try to understand what your reader will be thinking when they read it. How do you want the reader to feel? What information do they need to know, what information can wait until later?
When you don't feel like writing, read. When you feel like writing, write. Do lots of both. Watching shows/movies can count as reading too, or playing a VN. If you have a favourite, play/watch/read it again from time to time, every time you will understand a bit more about the decisions that make it great.
Keep this habit up and you will know how to write.
