You should be prepared to allow your ADHDer to make mistakes and fail so you can use the experience as a teaching tool. Often parents come to my office seeking ways to keep their ADHD child or spouse from failing at something.* As I tell them, if a child never falls down while trying to walk, the he will never learn to pick himself up and keep on going. Failure provides learning experiences. My hero, Walt Disney, reportedly bankrupted more than once, but look at the legacy he built through learning to adapt to failure and mistakes.
You must let them fall down and teach them how to pick themselves up. Once you do so, then it will be much easier to teach them how to avoid falling down in the future. ADHDers are usually really good at remembering mistakes and shortcomings, so one simple reminder of a past event may be enough to prevent or stop a current anger crisis. When teens get a speeding ticket, most parents take their license and car away. A smart parent sends their teenager to a driving school* designed to teach skills to cope with impulsivity, such as building a habit of glancing at the speedometer and correcting speed. Taking the car away doesnt correct the problem and produces more frustration and feelings of loss of control.
Be sure to remind your ADHDer that everyone makes mistakes, so they are considered normal.* More than anything, ADHDers want to be perceived as normal.
*
http://www.drhuggiebear.com/helpingteenagers.htm
This thread has been a well... experience for me but I am determined to keep it alive for as long as I possibly can. Anyone who has a question feel free to ask away I am pretty knowledable. 
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