When you make a request of your child, and he does not comply, take these steps:
Give one reminder. Say, 'What did I ask you to do?' If your child responds correctly, say 'Good. Now do it.' If he doesn't respond, then get his full attention and tell him one more time, being very specific and firm.
If he whines or argues or stomps off, simply ignore him. Walk away with the attitude that you are certain he will comply. If he doesn't comply with the reminder...
Stop everything and give one warning. Now is the time to tell the child what the consequence for non-compliance will be. This is it, you will not warn him again. Don't show anger, instead be very matter-of-fact and calm.
Now, walk away again, keeping the eyes in the back of your head open to watch for his compliance. Don't escalate a confrontation or stand over him with your hands clenched at your waist. Convey your assurance that he will make the choice to comply. If he doesn't...
Implement the consequence immediately. It may be time out or removal of privileges. Good consequences should be brief and related to the misbehavior. Give a consequence that is unpleasant to him, but not irrational or overly harsh. Just because he goes to time-out or has another consequence does not relieve him from complying with your request. The consequence stays in effect or is replaced with another one, such as early bedtime or no TV, until he complies.
Give him the opportunity to make amends. Defiant kids tend to back themselves into a corner. When he does comply, even after receiving a consequence, thank him and talk to him lovingly about why you made the request and why his cooperation is important to you and the family. Forgive him, give a hug, and go on about your day.
Be forewarned that he may escalate his bad behavior during the time that you are implementing this plan. He's trying to regain the control that he feels he is losing by complying, and he is frantically trying to return to the status quo. The purpose is to frustrate you and get you to give up. Stick with the plan and continue to practice relationship building, attending to the positive, and giving effective instructions and consequences.