I was diagnosed at a young age. I have some tips.
- When working on anything, focus on that task only. Close any unnecessary tabs in your browser, put your status to "away" on IM clients, turn phone on silent, etc.
- Unsubscribe from any email newsletters, updates, etc that you never read anyway.
- Remove clutter from your computer desktop and form your actual desk.
Here's a good book to read:
http://focusmanifesto.com/
Here is the author's blog:
http://zenhabits.net/archives/