Its far more easier to decide to work from home, then to actually do it for real, and having done it for approximately seven years (no longer as it doesn't fit in with my current career), I will now give you the guidelines according to Thomas.
The are a number of non negotiables that I abide by when setting up to work form home (I may be flexible on other matters, but remain totally firm on these):
1. Dedicated space for your home office.
Normally I allocate a bedroom and kick the bed out (at the most, the bed replaced by a sofa bed). By making a room exclusively your home office, means when you walk in, mentally you are at work.
2. A proper desk / work space.
This space is to be used for work, and work alone. No using the desk for your partner's hobbies or for you to store perhaps your magazines.
3. Suitable hardware.
Think about all the various office hardware you would normally use in a typical office situation... now, ensure you have the same in your home office (eg. If you use a fax, then implement a fax solution into your home office). If you short cut the process here, your work's efficiency levels will surely take a hit.
Similar to hardware, if you use a landline as part of your business, ensure a landline is present in the home office ( a dedicated one at that), and don't forget a fax line, if the obligatory fax is used.
A dining room chair just will not suffice. Companies don't provide ergonomic office chairs for the sake of it. That sofa bed I previously referred to has another purpose... visitor seating.
6. Air conditioning.
Most offices have their air conditioning set at 22.5 degrees celsius (apparently the optimum working temperature for office workers, or so I have been led to believe) so here is another area that must not be overlooked.
7. No house work during working hours.
This is a critical one to remember, so easy and logical, but many people use house chores as an excuse to take them away from their office work. Ask yourself a simple question... is it work related? If not, it is to be overlooked.
8. Dress for work.
Yes, sounds simple enough, but so many people forget this little detail... if you dress for work, it helps you to get into work mode. It may not be a suit as such, but adopting a certain dress code will always aid the process of working from home.
9. Schedule in some time with colleagues.
Humans, being the tribal species we are, love company, and it is the same in work. Perhaps once a week, go back to the office, even if it is for half a day, and mingle. Your work at home ethic will benefit as a result, and be easier to sustain.
10. Keep normal hours.
If you work an 8 hour day normally in an office environment, then a similar working day, at home, is totally appropriate, and not a 16 hour day. There are many good valid reasons for working from home, but longer hours is not one.
So there you have it, ten tips for working effectively from home. Use this as a starting point, and build from here. I hope it helps, and if you are lucky enough to be in this position... good luck.