* If you share your home, make sure that your cohabitors understand you really are working when at home. While that may sound obvious, it will help you draw a line in the sand should they ask you to be in for a delivery or repair person, etc - those things can be a real flow killer.
* Make your home office a separate room, if at all possible. If the door locks, so much the better: there will be times when a locked door will help you (either keeping others out or giving you that extra subtle indicator that stuff needs to get done).
* Have a clock on the wall - it's a cheap, simple, subtle way to increase the 'work' feel of the room you're in, plus it's a change in the depth of focus after hours of screen-distance reading.
* Take breaks, get out of the house.
* Participate in some kind of community chat (IRC, HipChat, Campfire whatever) to prevent going insane. Consider rationing your time on that chat, rather than having it as an open channel.