Above all, DON'T PLAN your stories before you start (unless you like doing them that way). Just sit down and write what comes into your head.
This is called VOMIT WRITING.
You know how, when you are sick, what comes up is a grand mixture of everything? (Usually including carrot, even if you have just eaten greens? YUCK!) Well, writing is like that. You need to 'sick up' all your thoughts and daydreams, then sort out which are the best ideas for the story you want to write. If you have any ideas that don't 'fit,' save them for other stories (put them into a 'spare ideas' notebook).
This is a bit like separating out the carrots from the chocolate cake and the strawberry ice cream: it's all good stuff, but needs to be 'unmuddled' before you can work with it.
Once you have this rough story, then look at it and see if you can shape it using a structure like the one I have given you, or take a planning method you have been taught before that you like, then look at your story again. Does the plan help you pull your story into shape? If it does, then adjust your story.
This is called TROUBLESHOOTING.
Some people like to plan everything out in detail, but most people work best by 'playing' with ideas and words until something good starts to emerge. You can't plan until you have something to plan with. What's more, it spoils the fun of writing if everything has to be carefully planned before you start. Stories often like to 'do their own thing' and often end up much more exiting and take you, the writer (and the reader) down much more exciting paths if you give them their head!
Once you have a good idea you like, you can then make sure it follows an interesting and fun pattern with plenty of excitement and action in the right places, and then you can rewrite a really well thought-out second draft.
I write like this, and so do quite a few famous authors. I am pretty certain Terry Pratchett is one!