Some great answers here (I find AmericanOP's the best).
Not a complete answer from me (and not formally diagnosed, but I strongly relate to everything mentioned here), but here is a list I have called "Things that help with work"
Before work:
- Wake up early (but not at the expense of good quality/quantity of sleep). If possible, without an alarm clock.
-Start the work day as soon as realistically possible, before distractions start piling up
-Start with the hardest task. Not the easiest (unless it's an easy part of the hard task). (doing unrelated but useful easy tasks may be a good strategy when tired/unfocused, but at the start of the day it will probably end up wasting valuable limited energy and being counterproductive)
Preparation / During work:
- Drone Zone / ambient coffee shop sounds, or mellow coffee-jazz on youtube
- tea (chamomile/passionflower/melissa or other similar distraction-mitigating beverages). coffee can be positive or negative depending on energy / time of day.
- Water. Lots. Easy to forget, makes a huge difference.
- Oxygen. Lots. Also easy to forget, also makes a huge difference.
- Use pomodorros: a 25-minute slot where you commit to uninterupted focus on a task, delegating any distractions to be dealt with after the pomodoro.
- For added effectiveness, commit out loud to do "Task X and only task X, to the exclusion of all others" before you click 'play' on the pomodoro.
- GTD to keep track of and prioritise tasks effectively
- Log work done in work diary (with regular desktop prompts to do so if necessary). Helps you more easily pick up from where you left off.
- incense, for some bizzare reason. (assuming able to keep window open)
- air heater (WARNING: counterproductive in the abscence of oxygen!)
- undistracting view
- study-buddy
- Pleasant location, preferably with other people working / not interested in you
After work:
- No work after X time
- Plan ahead. If possible, also plan "where" to work, based on the task - choose best environment, create positive association/mood for work
- Sleep. No "revenge procrastination". Ensure that if you wake up reasonably early tomorrow, you will still have gotten enough quality/quantity of sleep. Lack of sleep compounds very easily.
- Rest on weekends (pet projects are fine, but not "work" work).