Well, first I have to either be inspired by something or come up with a unique idea to write about. Next, I just write down what comes to mind when I think about that idea and my opinions, emotions, and questions towards it. Then, I organize all those ideas into something with a good flow, good punctuation and grammer( it's ok if you aren't good at that, I wasn't at first either but I have improved a lot since I started writing; it just takes practice), and something that reflects how I feel about a certain topic or concept ( or in the case of a story, how the character feels).  Also I read a lot so I know about good sentence structure and what makes it flow and what doesn't. I also write a lot and it has become very natural for me to write and it is second nature to me to write. Plus, for me I can be very passionate and think deeply about a lot of things so I just try to express that in the best way that I can. It also helps to join a writing club at school, or write for your school's newspaper, and just surround yourself with good writers that can help and support you. Also, one huge thing that can help is to PAY ATTENTION IN ENGLISH CLASS!!!! It own't necessarily help you with stories but it will help a lot with essays, poems, grammer and punctuation. That is mostly where I got some of my writing skills from. Hope that helps!! :D

P.S. sometimes the best thing to do is to not think too much about what you are writing and just write something, even if it sounds silly at first, because then you have something to work with and you can always edit and change things later if you need to. :D