The best thing to do for back-talk is to completely ignore it. By that I mean you deliver your request (e.g., please pick up toys, turn off the TV) calmly but firmly and then you say nothing else. Any negative behavior that follows (or precedes) is handled with a straight poker face. Make no eye contact. Turn your body away. Leave the room if needed. It sounds crazy, I know, but this works. It won’t happen overnight, but if you stick to this, it will turn things around. The reason it works is that kids (and many adults I know) seek out negative attention. They love to argue because it gets a reaction. So don’t play into their game!
Generally, when you do make any request of your kids, make sure they are making eye contact. Ask them to repeat what you said or else there’s no accountability. And attaching a consequence to your request strengthens this. The consequence doesn’t need to be delivered right away. It can be something later on. They can earn or lose something like t-ball, swimming, a playdate… anything that motivates them to change their behavior in the future. The trick to better parenting is less emotion and letting the consequences (good and bad) do the work.