I've been telecommuting for ~20 months now. For me, the key things to do to stay focused and productive are: separate work from the rest of your life, have a plan of what you are going to do next, and have a plan for dealing with the inevitable times when you become unfocused.
To keep life and work separate, you can have an office that is only for work (no gaming/web surfing), or, if that isnt in the cards, have a different computer. I really like having the work computer run a different OS. Linux is for work. Windows is for play. That way I am not tempted, and I have that sense of 'being' at work/
Having a plan is crucial to keeping going. If you finish something and think 'what should I do now' youll be reading slashdot within seconds. I try to do my planning at the end of the day, so I have a nice list of bite sized tasks for the next day already waiting for me.
Despite my best efforts, sometimes I realize I am not focusing on work. When that happens, I have a few things I can do to get refocused. The first is to change desks. A change of scenery and position (sitting vs standing) is nice sometimes. Next, I can make coffee. It takes a few minutes, so it gives me a chance to psych myself up, knowing that when the coffee is ready it is time to get back to worrk. Finally, I have ear protection, usually used while chainsawing etc. When I put it on, I cant hear anything but my own breathing, and focusing on your breathing is a common meditation technique, so maybe tat is why it works. Anyway, it really quiets the mind and gets me back to focusing on work.