One of the biggest reasons I see parents struggling to manage behavior problems is due to their lack of confidence in their parenting skills. I don't know how often I hear a parent say, "He's just not going to listen anyway," and they give up on setting limits with their child.
This can be dangerous territory. After all, if you don't think your child's going to listen, I bet he's not going to. Your tone of voice and body language will likely convey the message of, "Please, please listen to me because I don't know what to do if you don't listen." Even if your words say otherwise, the way you send the message will speak volumes.
Kids are smart. They learn pretty quickly how to push your buttons and what they can get away with. So, if you usually don't follow through with consequences, they'll call your bluff when you threaten to give them one. Which can make a parent's confidence in their discipline strategies get even worse.
It's important to break this cycle. Take a parenting class, read some parenting books, and get support from other parents. Do whatever you can to gain more confidence in your parenting.
Learn more about why it is important to set limits and start setting those limits right away.