It means to say or do something sooner that it should be done and as a consequence the proper preparations or explanations for it are not made. Example: "When he decided to buy this house before getting hold of the money, he got ahead of himself ."

"Don't get ahead of yourself."= Don't try to rise above your station [ status] in life or "don't get cocky" Another meaning is "don't celebrate too soon"

Don’t do anything that is not yet ready to be done or more importantly don’t do anything beyond your current ability or position. To act prematurely or to be overly confident or to get carried away ( with excitement for example) Let’s say you are learning how to drive. You can’t wait to get on the road and drive on your own. You need to be patient, finish learning how to drive. You can use it the other way around too, when you say or do something that results in something slightly advanced that does not make complete sense. You can just say…. Oh perhaps I am getting a bit ahead of myself here….. Hope that helps

“Don’t get ahead of yourself” can mean more than one thing. Another meaning not yet mentioned in this thread is to focus on what’s happening now rather than rushing into future plans without a base. Because we won’t know our next steps until we complete the current ones and see what we want to do from there.

Don't do something too early, or before you are ready or prepared.