Be Mom and Dad first. Your love is the most powerful treatment any of us can imagine. If all the other stuff you have to do first interferes with being a parent, stop. Someone else can do some of the other necessary stuff, but nobody else can be Mom and Dad. Difficult behaviors result from unmet needs.
Difficult behaviors are expressions of real and legitimate needs.
Don't assume anything. It is easy to make the mistake of underestimating your child's potential because of his or her labels or because he has failed to acquire certain skills. This is a tragic mistake. Always speak directly to your child and explain things as clearly as you can. Afford him the same respect you afford to your other children.