Take out a calendar (preferably a huge calendar with big squares!) and X off days when you are absolutely not working, such as Thanksgiving day, Christmas day, the last day of Hanukah, days when you are in travel status, etc.
Then, put a line or note through the days on either side of those. Let's be realistic with our lines--although you could work the day before Thanksgiving, will you? However, notice that I don't advocate that you block off these days altogether. That's because these days are actually pretty good days to manage emails and other small administrative tasks. This helps you to avoid a backlog on January 2.
You are now ready to more realistically take on and schedule projects. Days with large Xes are not available, and days with smaller lines are only for email, adminsitrative tasks and maybe some social networking. Remember, the key to time management for writers is being proactive.