Prepare for the journey
Some stories you can leap into with little or no preparation, though they are less common than you think. Even if you are writing a book based in your own neighborhood, it won't hurt for you to think about and jot down a few things like descriptions of places and people. The farther from your 'real world' you wander, the more background work you should do before you start writing. Getting the setting and a few of the rules of how things work created before you start the story can save all kinds of trouble in the writing. It will also save you considerable time in rewriting.
You do not need to write an outline. I do, because I like to have a roadmap of where I'm going. A couple lines per chapter can be enough to get me there.
Ready, set go!
In order to be a writer you must write. You must sit down and put the words on the page -- and make no excuses for lazy muses and writer's block.
Hint: if you write more about writer's block than you do about anything else, your attention is in the wrong place.
If nothing else, sit down and write 100 words. Then do it again. You'd be amazed how fast those 100 words add up to something useful. 100 words is a small enough block and you can focus on those few words of the story and make something of it. Do this three times in one day, and in the course of a year you will have written a novel. You think it's too difficult? Then maybe you aren't cut out to be a writer. For a comparison, this paragraph is about 150 words. Don't tell me you can't write that much.
We often do 100 word leaps in the 'Write with Zette' the Forward Motion chat room where I often hang out. We also talk about writing and other things --but we mostly write. Sometimes it helps to have others by you, urging you on or just discussing writing in general.
Another hint: Read about how other writers work, even if they don't appear to work the way you do. You never know when one little thing is going to make a difference in your own habits or in the quality of your work.
I write fast first drafts. There's nothing wrong with writing fast. Rex Stout of Nero Wolfe fame wrote very quickly, among many others. However, always remember that first drafts are a gift of the writing gods and are not expected to be perfect. We are allowed to make mistakes. Don't let it stop you. Keep writing and stop making excuses not to finish.
You don't have to write quickly. No one has to write in anyway except what suits them. I suggest 300 words a day so you can have a manuscript in a year. I write over 3000 words a day. My way is not your way.
And yet another hint: You are going to learn more about writing from finishing something that gave you trouble than you will from any easy story you complete. If you give up because you lost interest in the plot and characters, go back over it and find out why it no longer appeals to you and fix it. If you wrote yourself into a corner, delete some words and go a different way. Giving up should never be an easy option.
Taking a rest
Once you are done, let the story rest. Move on to something else before you edit. If you leap right into editing, you are less likely to see your problems because you still have the image of the story in your mind. Let it go by writing something else.
This is not (despite my analogy here) a race. You're also never going to achieve anything with only one story, so start preparing yourself to write more. Jot down notes when something occurs to you. Build up a backlog of ideas, but don't let them take over.
Going for the next lap
Stop dreading the idea of editing. Stop expecting it to be horrible work and the last thing you want to do. This is your chance to take the original vision that sprang from your head to your fingers and make it more of what you really want it to be. Play with the words. Play with the style. Take it slowly. I usually edit two to five pages a day on a story, and go over those pages several times.
I also write something new while I'm editing an older piece. This doesn't work for everyone, but if you can, it allows you to have the fun rush of creation that so many authors crave and will make editing far more fun.
Taking another rest
Once you think you are done with the entire process, put the story away for a few days -- or, if you are inclined, now is the time to have it critiqued. No, not before this point. Never send a first draft out to be critiqued. You'll look like an idiot and you will waste a powerful resource besides. It is up to you to make all the corrections you can before you allow anyone else to read the material. If you send it out too soon, you ruin a critique for a later version. You never want a person to have some preconceived idea of the story, especially one based on a messy first draft.
When you are ready, either after a critique by others or just having let it sit, read one more time. Make last corrections.
Give it Wings
And now it's time to let it go. This might mean writing a query letter, sending sample chapters, sending an entire short story or preparing for Indie Publishing. Whatever your choice, make certain the story is the best you can make it before you send it out to readers of any sort. Don't rush and set it free too early.
Be wise and be willing to learn and adapt how you work to do better.