I have ADD as well. What works me best is a timer.
When I started this, I would set my timer for five minutes and work for only those five minutes. When that was up, I would reward myself. I continued doing this until and slowly increased the time; thereby training myself to work for longer periods.
I now bounce between 15 minutes (for when I feel antsy or weekday evenings when I have several different tasks to work on), 30 minutes or an hour (when I'm feeling pretty driven and I have a major project I'm working on). Most places I've seen recommend that you work no more than an hour without breaks.
This may sound like you won't get anything done, but you will be amazed at how much you can get done in just 5 minutes.
I had ADD well before anyone could tell me what it was. And I KNEW that I had a problem most people didn't, I just didn't know what it was. When I found out what ADD was (after I graduated college) I was finally able to deal with it effectively.
Getting organized - lifehacker.com has some great suggestions, but I really recommend you start with a to-do list of some kind. It could be a word document, a 5x7 card stack, or an online to-do - find what works best for you. This is how I get organized at work.
You don't have to finish one item on your list before you start another. I often leave projects in the middle and go do something else. This keeps me from getting overwhelmed with everything I need to do.
Minimal distractions. I don't know about you, but very few things use all of my brain. I find that if some part of my mind is being ignored it can become the biggest distraction of all. So you need to figure out what are your distractions (for me, it is anything in print and anything that moves), and what can calm that part of the brain that wants attention. Again for me, that is music and I find that photographs of outdoor places also calm me down.
Notes I write straight onto my to-do list at work.
Another ADD specific point. It's easy to get into a what-to-do Catch-22. You need to wash the dishes, but you need to pay bills, but you need to do laundry, but you need to get the dishes done...
The way to solve this is to choose an arbitrary pattern. I go around my house clockwise (one room per time block) even if the bedroom just needs picking up and the bills are overdue, I'll still start with the bedroom and ignore the bills till I get to them.