What do I do if I dont complete a task that i want to do by a certain of my choosing deadline?

Let me explain: So I'm trying to be more responsible with self imposed goals. Things I wanna do and learn however I struggle to stick to a deadline. What are some ways I can stick to to that self imposed deadline? What should I do if its something I need to do but I miss my deadline? I'm afraid I'm a bit too laid back. I hope you all can understand what I mean. I'm not sure if I explained it correctly.