I have three daughters. My eldest, who is 11 1/2, has ADHD and ODD. My middle, who is 9 1/2, has Autism, ADD, mild ODD, lactose intolerance, learning delays, seizure disorder, and some other related issues. Prior to starting Concerta (ADHD) for one and Intuniv (ADD) for the other we put many behavior plans and expectations in place. In addition to that, we have found the Feingold Diet to be a godsend. An absolute blessing.
Please look into the Feingold Diet. It's essentially about eating as naturally as possible and avoiding highly processed foods and foods with a lot of chemicals in them... ie. food-like items. It's also about identifying trigger foods and ingredients that your child's body is allergic and sensitive to that should be avoided and could be causing more than just physical symptoms but behavioral symptoms as well.
For instance, High Fructose Corn Syrup and artificial food dyes such as Red 40, Blue, and Green are the worst offenders for my daughters. Their kidneys and livers can't filter out these toxins nor metabolize them, so they coarse through the system until the body expels them. During the time that they go through the body, including the brain, there's emotional upset including mood swings with anger, misbehavior, hyperactivity to an extreme, nausea, headaches, dizziness, and at times vomiting. If my eldest gets Red 40 on her skin because it's in a lotion then her skin swells and puffs up in allergic reaction. She vomits up Christmas cookies and red velvet cupcakes.
Removing and minimizing these things has improved their behaviors more than I can say.
Anyway, my best advice is to research the Feingold Diet.