Big +1 on this one. It's essential that your family/friends/etc recognize that when you're in there you're "at work" and need to be treated as such. That being said, be flexible if your company is. Sometimes when working from home I'll run and pickup my kid from school even though my wife usually does that. Just because he'll think it's cool that dad picked him up and it's a nice break in the day. My work is based on accomplishments, not hours so I have that flexibility and I use it.
Couple of other things:
1) Get ready for work! Don't just slump out of bed and jump in the chair. Eat breakfast, take a shower, get dressed. You'll be more productive, I guarantee it.
2) Don't get caught in the trap of working too much. When your work is at home it can be hard to walk away from it. If you're done for the day, stay done.