Courtesy of the enchanting Mason Bundschuh, I now have a sign under my computer screen that says:
Stop Twittering and Write.
You'd be surprised how much this actually helps me. Since I put the sign under my computer, my writing productivity has increased by 100%.
If you're like me and get distracted by the shiny internet shortcut on your desktop, then having things that distract you away from Twitter, Blogger, and Facebook are actually rather successful.
I recommend printing out quotes about writing, quotes from books you love, motivational one-liners, or anything that makes you want to write. For my current work-in-progress (a.k.a. NaNoWriMo), I have the thing that inspired my story in the first place sitting next to my keyboard: a metal candy tin. When I see it, it reminds me of my story and gets me excited about writing again.
Whatever makes you want to write, surround yourself with it. Tape it to your desk, to your wall, to your keyboard... put it somewhere you can't help but see it. Now, stop reading my blog and write :P