Unable to write? Feeling distracted?
Well, you could always step away from your project and go for a walk or something. But that's really just another form of procrastination. Try writing about what is distracting you. At the very least, just start writing gobbledygook. Eventually you'll tire of this and your imagination will take over. Before you know it, you'll be back on track writing up a storm, or a cool summer breeze, depending upon the nature of your project.
Don't let the quality of your writing concern you too much at this point. Don't allow yourself to get caught up rewriting. Produce new content and keep going until you get to the end. Then go back over it and refine what you've written. There's time enough for polishing your prose once you've brought the plot to its appropriate completion.
Here's a short film on the subject: