While I am sure most people have their own techniques. I always try to define the idea. That kernel of whatever the future project is going to be. Just get the words out of my head and onto the page. Once you have that the words just begin to flow naturally.
I find it also helps if you think of trying to explain the concept to a Tibetan monk who has been isolated in the mountains for one hundred years and has never seen anything like your idea. If you can make that person understand, anyone should be able to grasp what you are talking about.