If you're having trouble cranking out that masterpiece, one technique I like to use is timed writing exercises. Give yourself 10, 30, even 60 minutes where all you do is write without interruption or distraction. This may mean writing with the door locked, the phone taken off the hook, and your email alert put on mute. Whatever it takes, do it.
Try to make the environment around you disappear so you can focus 100% of your energy to the story, journal entry, chapter, or poem. Keep a piece of scrap paper nearby so when you remember you need to buy onions at the grocery store you can quickly jot it down and throw the thought out of your head, then get back to your writing. Time your writing and see just how nice it is to hone in on your creative juice.