i get in a bubble bath with a board across the tub and some wine, and maybe a candle, with my iphone to look lil things up, and my books next to me, and maybe a lil 420 as well. once relaxed i just start imagining, and write one thing down, then flesh that one line out with details.

One thing I'd add to the wealth of advice you've received thus far is to constantly remind yourself that you're preparing for a game and not writing a novel. Elaborate histories, back stories, and all the stuff of world-building can be enjoyable for a gamemaster as a kind of side-hobby unto itself, but most of that work will never see the light of the game table.

I concur with those who recommended picking a low-level module that you like and running it. Forget grand ideas about a "campaign" for now. Ideas for the next adventure will most likely arise from events created by the players themselves during the module adventure. At this point, just remember the above rule and focus only on the next adventure. This can be another module with a bit of transitional writing created by you to make it fit or better yet, pick an "Adventure Path" created by companies who write complete story arcs.

From this experience you'll gain insights into what you would have done differently, what you'd like to see happen, and so on, as well as experience with how adventures are scripted and structured -- all while immersed in the act of playing the game itself rather than "studying up" on how to write.

Personally, I don't write campaigns as campaigns. I write them like short stories, then use them as guides for my campaign. I also try to do a "goal sheet" of key events the PCs need to hit. Outside of those, I rely on what my players give me to work with; back stories, ideas while on break (I miss my weekend long games...), and even the random dumb idea (respun of course).

What I'm getting at is don't try to think as a DM. Think like a writer.

One more tip, something that helps me: you don't have to make every post an epic.

I can often think of a short stat of a post but no idea for a middle or end, especially when reacting to players.

In these cases, in stead of pondering for days or waiting to get in the right mood I have learned to just write. Just start writing something, and very often something else flows as the right part of your brain switches onto it.

You might not get the best possible result, but it will be better than you think. It helps to keep the game moving and that is often far more important.