Make sure that the person's strengths and capabilities don't get forgotten when reducing or eliminating challenging behavior. Instead of ultimatums, give choices. If the person uses challenging behavior to express needs, give the person choices and allow the person to make choices throughout the day. Choice does not mean free rein. Set limits with the input of the person with a disability.
Every relationship has limits.
Help the person to have more fun. Fun is a powerful cure for problem behaviors. If not, look for things the person enjoys doing. Add to that list. Make fun a goal.