I can relate what I've learned with regard to writing, which I believe holds true for many creative endeavors (including creating setting, characters, plot, etc.). There are three lessons that I can convey to you, which may or may not help.

The first is, very simply, Do. Dive in and get started. Sit there, over your pad and pencil, or typewriter, or keyboard, and start doing whatever it is you're going to do. Wanting to do, planning to do, thinking about doing - none of that is enough. To quote Yoda, "Do. Or do not. There is no try." The same holds true here - until you actually sit down and get started on your task, it makes absolutely no difference what you want to do. Just paraphrase the sporting shoe slogan and do it.

The second is less simple: Abandon quality control. Just temporarily, mind you. Many people encounter what is commonly referred to as writer's block, and I have no doubt that you're suffering from a bit of that. I attended a lecture once, and the speaker vocalized a point that many creators think about, but fewer can put to words. That point is this: The creative head wears two hats, creator and editor. The creator produces work, and the editor refines it and filters out the rubbish. The problem is when you try to wear both hats at the same time; you end up dismissing your work before you can even put pen to paper. Thus, my second piece of advice is this: Write a crappy first draft. I mean, write at the top of the page, "Crappy1 Ideas." In doing so, you abandon any attempt at quality control - that will come later. Having set your standards aside for a moment, write down everything. And I mean everything. No matter how silly, no matter how absurd, no matter how obnoxious or repugnant, it all goes on paper. And you sit there and write everything in your brain until your pen has run out of ink or your brain has run out of cells, whichever comes first. After you do this, you can start quality control. And I guarantee you, while 90% of what you wrote may never see the light of day, the remaining 10% will be stuff you can use.

The third lesson is as simple as the first, and it is this: Don't stop. Once you've started, you've gotten over the hard part. Inertia is a very real thing; ask scientists. But just because you've started running in the race doesn't mean you've crossed the finish line. Creating is work. People actually do it for a living. Even if it's just a hobby, you need to devote yourself; if you're not passionate about creating, you're going to run out of steam in a snap. Keep at it. New idea? Write it down, integrate it into the setting. Find a plot hole? Go back, revise, fix it. Clever character concept? Work it in somewhere. You can stop at any time, but you can't guarantee that the work will continue without you. Be prepared to see it through to the end; devote a certain amount of time on a regular basis to making sure it gets done.

And that's it. Three lessons. But it all starts at the same place, putting one foot in front of the other. Creating is like walking, and you've got to walk before you can run, or fly. Step one is to simply start; the rest will follow, if your heart is in it.

1 You are free to use a different word. The lecturer used a much stronger four-letter word. The idea is the same; the word reminds you that you're not attempting quality control.