Instead of ordering your kids to do a chore, give them options. Ask if they want to do a task now or in a few minutes. Ask if they would prefer to take out the trash or empty the dishwasher.
Kids fight back when they feel like they have no control. Resisting you becomes a way of asserting themselves. Giving them some say will help motivate them.
Plus, giving them choices now teaches them how to make healthy choices later.