Anything on paper is never going to look or feel exactly like it looked or felt in your head. When you imagine a story, your brain comes up with feelings as well as words and pictures. But when you put the idea down on paper you can only put down words and pictures. Over time, with trial and error, you can figure out what words and pictures to use to communicate some of those feelings back to yourself and other people. But it's not automatic, you don't just imagine stuff and then write/draw it and then feel exactly like you imagined. That takes a LOT of work and learning and trial and error.
If you want to be good at writing or drawing, you have to be bad at it first. That's true for everybody. You get your ideas down on paper, you expect them to suck, and then you go out and try to find ways to improve them. Over time you learn more stuff and you do better. But you can't just "do better" from the start, you have to make the mistakes and then learn how to fix them. Waiting until you can just do it perfectly from the start means waiting forever because you can't get better just by thinking about it. You have to do it and suck at it first.
First, make notes of all these ideas, there may come a time when you are short on ideas (SERIOUSLY, it happens)
Next, work on the skills to do what you want.
Have you spent time on the basics: Shape and form Perspective -1,2 and 3 point to start Light and shadow
Those are the basic building blocks, kind of like you alphabet of art. Then you have the fundamentals, they build on the skills learned from the basics: Anatomy - rocks and plants have anatomy too, not just people Composition Color theory- if you are going to work in color
To get from where you are now to where you want to be, you will need to decide where your skills are deficient and start to work on the skills to do what you desire. All the artists you admire were at your skill level at some point. They all got better through hard work.
Do you know how a story is structured? Look at books or a comics, or at movies, and analizew them piece by piece. When I write, I use this scheme: conflict-reaction-conflict-reaction-conflict-reaction. It seems stupid, but most comics, books and movies are structured this way. Conflict need to be greater while the story goes.
Also, do you know your protagonist well? What are his motivations? are they strong enough? Not all our OCs are adapt to be protagonists, some are better as secondary, or even background characters.
First drafts/ firsts sketches are almost always rubbish - you have to do the work of editing and refining, but that's ok, just get the ideas down and worry about polishing them later.
If you see it in words and pictures, write it that way, either as a comic, or as a story with drawings interspersed through it.
Go have a look at some kids easy readers that have pictures in them - they don't have to be masterpieces, they just have to get the point across.
The only way you get better at these things and start to be able to write and draw what you imagine in your head is with practise, just do it, don't worry about the outcome, enjoy getting the stuff down on paper, you can worry about making it good when you've done enough of it that you feel like you can go back and edit.
Also, don't forget, writing and drawing are skills, there are resources out there to help you learn them, and while it might seem daunting, don't look at it as a mountain, just look at it as a path, and every step on the path gets you somewhere.
you are going to screw up, and that's okay write it out, sketch it out first don't worry about how it looks like
edit and adjust the lineart later work on it bit by bit for drawing, use references/stock photos, they help you draw more realistically... for writing, read books -- see how your fav authors do it and little by little you will start to see something nice appear on the page
I had the same thing happen with writing too. I wait until I have the motivation and inspiration to write and don't force myself, unless I want to write a whole load of nothing and get discouraged. Even if it makes no sense, write down everything you picture in your head as quick as possible as if you're retelling a movie you're watching right now. Easier said than done, but still. You can have time to fix up punctuation and grammar after getting the basics. The quicker you get into it the better you'll be
Okay I didn't help much, if at all. Good luck, though
But for drawing, if you can see it in your head there's no reason you can't execute it. If it's not turning out how you want immediately then work on it until it does. The only reason one can't draw what they see in their head is just lack of patience + determination.
save stories for when you are a touch older. I couldn't commit to long term storytelling until my 20's (not sure how old you are) still, ideas wont get stale in your head. draw single illustrations now like OC's cause while you draw your characters over and over you think about them more and more and you can then apply these neat characters to whatever story you're formulating. Plus single illustrations are good for practice and short attention spans.
If you're fond of writing I would start writing little short stories and maybe illustrating them. Comics might even be a good route for you.