Working from home can be a curse and a blessing. The curse part is that you're at home and home things are always beckoning you away from work, and vice versa. One sure thing is that if you have a room to call your own, you need to make it an attractive and efficient space where you want to spend time. And if you've just blown the budget on a new furnace, don't worry, these tricks cost practically nothing.
1. The first thing you need to do is to put some art on the walls. Don't use old posters you've had around the house. Find some fresh, new, inexpensive art posters and use an old frame you have. Better yet, go to Michaels, buy a canvas with one of their weekly coupons and paint your own art with a pack of acrylics. (I've got my own art all over my work areas.) Take a look at this Curbly post on DIY Font Wall Art.
2. Take everything out of the room and start fresh. I always struggle with moving things around in a tight room, but I don't have so much trouble when I start with an empty room and add only necessary pieces, one at a time. If you've got leftover furniture, consider NOT stuffing it back into the office.
3. Remove everything from the room and closet that is a homey/family item. Even purge the closet of blankets or extra clothes. Make the closet a storage spot for office supplies. You need to feel like you're at work, not up in the spare bedroom.