This is a question that often arises, and in a writing book it's not really a big deal, but it's asked so often I thought we should look into it.
What can you do to write a better story? Anyone can write a story, but not everyone writes a good story.
These tips aren't in any order, but they are what you'll hear when you ask.
1. Read books about writing. Like this one. Like Stephen King's On Writing. There are dozens of guides, and the more you read, the more you'll know.
2. Keep writing. Most of aren't blessed with the capacity to run a marathon without having ever run further than a mile before. Sure, it might take us a lot of miles to get to run 26 straight, but they are all important, and they all help to refine and develop voice and style. The more you write, the more you get the bad out of the way to make room for the better.
Think of it like learning to color. At first you're just scribbling wherever. Then, once you've done that, you start to think of different ways you can color. in the lines. With shades. Blending.
3. Acknowledge your weakness. And no, I don't mean the "I'm too much of a perfectionist" or "I doubt myself" bullcrap. Eat some humble pie and take an honest look at your writing. You know what's wrong, the same way you know when you're hungry. You know you can improve. That's why you're asking!
4. Research your weakness. Grammar not so good? Are you having trouble plotting? The internet and your fellow writers are valuable resources to learn more about this! The more you know, the less mistakes you'll make, and the stronger your writing will become.
5. Practice your weakness. It's not going to do you any good to sit around and say "Oh, I'm bad at Grammar." And then complain when you aren't getting the praise, reads, or attention that you expected. You practice, you learn, you grow. You can know all there is to know about diving, but if you never go in the water, you might be surprised that first time you do go in and find yourself *not* perfect like you'd expected.
6. Read regular books. There are lots of ways to write. It's good to refresh your memory from time to time. There's some beautiful, inspiring prose out there! You might learn new ways to say something, or a new technique to describe a camel! Who knows!
7. Invite critiques. I know this is hard and scary and you're probably going to grit your teeth and grumble at least once, but sometimes we're blind to our troubles. We might think that we're really good with plot and just have bad comma placement, when really there are giant plot holes every where and the main character that's supposed to be kind is actually saying some mean things that you *thought* were nice.
8. Critique others. Sometimes, when you start doing it enough, you might find yourself sub-consciously learning and editing and refining your own technique.
9. Ask or research anything that comes up, when it comes up. Swallow your pride. Are you realizing that you need more help than you can give yourself? There are dozens of people who will happily help you! Or maybe you suddenly realized that you don't know how to write a good kissing scene. Go check it out! Read some! Practice! You don't only need to practice plot holes and grammar! There's more to storytelling than that!