Sometimes children don't do what we ask because we ask them while their mind is preoccupied with something else. One way to set your child (and yourself) up for success is to make the request and then ask them to repeat what you just said back to you. Encourage them to use their own words but don't get upset if they repeat back to you verbatim. Make sure your intention is one of creating clear communication and not of posing a threat or making them feel in anyway diminished. This also provides an opportunity for you to make sure your child understands what you are requesting. This is a loving form of reinforcement (and it works well with significant others too)!
By Kathryn Kvols, Author of Redirecting Children's Behavior and founder of INCAF