It is an amazing thing!
I learned this from the parenting classes through Gary and Ann Marie Ezzo called LET THE CHILDREN COME ALONG THE WAY.
Perhaps it will help you as much as it has helped me.
When you give your child an instruction (of any kind) have him/her respond ALWAYS with a "Yes Mom" or "Okay Mom".
This simple thing does something magical to my two year old! We can be at the park and I do the usual 3 minute warning..."We are going to be leaving in a few minutes so be ready when I call you to go cheerfully." I have him say, "okay mom."
Then, the time comes. "It is it time to leave now." I can tell he has heard me but doesn't want to and turns in the opposite direction." I call out to him, "child's name, Say 'okay mom'." He says it and magically his behavior follows! With no tears and no complaining!
Okay, it is not fool proof but I would honestly say 90% of the time it works.
This is why it works.
1) It shows you that they heard your instruction.
2) They seem to own it once they say it, therefore they become responsible for the follow through.
3) By verbalizing the right response it makes it easier for the proper behavior to follow.
Try it. I would love to hear how it works for your family.
And by-the-way, you can start this at any age! It is a bonus if you can start when they can only respond with a "ok."