If you happen to be feeling very motivated and enthusiastic about your story, then sitting down and writing it isn’t going to be a problem.
When you’re writing as fast as you can and all synapses are firing you really don’t need any particular structure or technique to your process. You write until you can’t write anymore, and then you get up the next day and do it again.
In a perfect world with plenty of free time and no distractions there would be no excuse for not getting those words onto the page. But things don’t always work out that way and most of us find plenty of reasons to give up and watch TV instead.
One method you might find useful if, like me, you’re not always delighted by the prospect of sitting at the computer with no end in sight, is to set yourself deadlines. Not just one, but many.