There are several ways a person can fix a squeaky leather jacket, including using oils on it and roughing it up with steel wool. There are leather oils on the market designed to help break the leather in, too.
When using a leather oil, rub it thoroughly into the elbows and other areas where movement is made, including the elbows. Do not overdo the amount of oil because it can discolor the jacket.
A leather jacket owner can also soften or break in the jacket by rubbing the shoulders and elbows lightly with a steel wool pad. This method softens the leather, which reduces the squeaky noises when the owner moves within the jacket.