The best thing that you can do is to learn all you can about ADHD, so that you understand what is going on with him.
The book I recommend the most because it answers so many questions in an easy to find format is - "The ADD/ ADHD Answer book," by Susan Ashley. Its only about 10 bucks on amazon.
A site that has a tremendous amount of good parenting ideas is this one.
http://www.additudemag.com/topic/parenting-adhd-children/parenting-tips.html
And by the way, the more that he understands how ADHD affects him, the better he will be able to cope with it. The same site has a great section on "schools and learning disabilities" which will be helpful for him.
Best wishes!