The best suggestion I can make is to stop doing other things. Turn off the computer, or take a laptop somewhere they don't have wireless. Don't play solitaire or bring a mobile phone. Then write.
It's amazing how much time you can spend not writing, without even trying. Make a rule that you can either write, or not do anything at all. (No TV. No long baths. No reading New Scientist. Staring out of the window is okay.) Pretty soon, you start to write, because it's more interesting than staring vacantly out of the window.
I need to go take his advice, and stare out the window until I get bored enough to write. :)