First things first, change your workspace if you can. This might mean using a different computer, sitting at desk rather than the couch, going into another room, or maybe leaving home to hit the library or coffee shop. I like a low drone of background noise so I used to get a lot of work done in Starbucks.
Then shut down the Internet. I like to keep a lot of tabs open to email, Facebook, forums, etc.and those tend to serve as major distractions for me when I'm using the computer for work. I think "I'll just check my email real quick" and twenty minutes later I find myself on Tumblr. Only open those tabs that are actually necessary for your work.
Make a list of tasks. I find this helps me keep organized with what I need to get done each day. The list usually includes homework, any chores that I have to get done around the house, my target word count for the day, blogs post I need to write, and anything else that I need to do.
Use a timer if that works for you. Some people find it helpful to set a timer for 30 or 60 minutes and then work the entire time. Then when the timer goes off, you take a break and start it again.
While you're working, give intermittent breaks--but preferably not the Internet. That's an easy black hole to get sucked into. Read a couple chapters of a book, watch an episode of a TV show, go for a walk, do whatever you like as long as you'll be able to come back from it refreshed and ready to work.